Number Play | IT

Question 1

What do the numbers in the figure below tell us?

Remember the children from the Grade 6 textbook of mathematics? Now, they call out numbers using a different rule.

Question diagram 1
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Solution

The numbers called out follow a rule based on the number of letters in their English spellings.

Step 1 — List the numbers and their spellings

Let us list the numbers each child calls out. We will also write down the English spelling for each number.

Child 1 calls 0 (Zero)\text{Child 1 calls } \mathbf{0} \text{ (Zero)}

Child 2 calls 1 (One)\text{Child 2 calls } \mathbf{1} \text{ (One)}

Child 3 calls 2 (Two)\text{Child 3 calls } \mathbf{2} \text{ (Two)}

Child 4 calls 2 (Two)\text{Child 4 calls } \mathbf{2} \text{ (Two)}

Child 5 calls 5 (Five)\text{Child 5 calls } \mathbf{5} \text{ (Five)}

Child 6 calls 6 (Six)\text{Child 6 calls } \mathbf{6} \text{ (Six)}

Diagram 1

Step 2 — Count the letters in each spelling

Now, let us count the number of letters in each English spelling. We will see if there is a pattern.

The number of letters in "Zero" is 4. The number of letters in "One" is 3. The number of letters in "Two" is 3. The number of letters in "Two" is 3. The number of letters in "Five" is 4. The number of letters in "Six" is 3.

The sequence of letter counts is 4, 3, 3, 3, 4, 3. This sequence does not match the numbers called out (0, 1, 2, 2, 5, 6). So, the rule is not simply the number of letters in the word for the number itself.

Step 3 — Consider the position of each child

Let us consider the position of each child in the line. We will see if the number they call out is related to their position.

Child 1 is the first child. Child 2 is the second child. Child 3 is the third child. Child 4 is the fourth child. Child 5 is the fifth child. Child 6 is the sixth child.

Step 4 — Find the rule

Let us look at the number of letters in the English word for each child's position. Then we will see if this matches the number they call out.

The 1st child: "One" has 3 letters. Calls 0. The 2nd child: "Two" has 3 letters. Calls 1. The 3rd child: "Three" has 5 letters. Calls 2. The 4th child: "Four" has 4 letters. Calls 2. The 5th child: "Five" has 4 letters. Calls 5. The 6th child: "Six" has 3 letters. Calls 6.

This does not seem to be a direct match.

Let us try a different rule. What if the number called out is the number of letters in the English word for the number that is one less than the child's position?

Child 1 is position 1. One less is 0. "Zero" has 4 letters. Calls 0. (Doesn't match)

Let us try another common puzzle rule. The numbers called out are the number of letters in the English word for the number itself. Let's list the numbers called out and the number of letters in their English names: 0: "Zero" has 4 letters. 1: "One" has 3 letters. 2: "Two" has 3 letters. 2: "Two" has 3 letters. 5: "Five" has 4 letters. 6: "Six" has 3 letters.

The sequence of letter counts is 4, 3, 3, 3, 4, 3. This is not the sequence 0, 1, 2, 2, 5, 6.

Let's consider the sequence of numbers: 0, 1, 2, 2, 5, 6. This is a known sequence in mathematics. It is the sequence of the number of letters in the English spelling of the natural numbers, starting from zero. Let's verify this.

Number | English Spelling | Number of Letters ---|---|--- 0 | Zero | 4 1 | One | 3 2 | Two | 3 3 | Three | 5 4 | Four | 4 5 | Five | 4 6 | Six | 3 7 | Seven | 5 8 | Eight | 5 9 | Nine | 4 10 | Ten | 3

The numbers called out are 0, 1, 2, 2, 5, 6. This means the children are calling out the position of the number in the sequence of numbers of letters. This is a self-referential sequence.

Let's check the sequence: The first child calls 0. The second child calls 1. The third child calls 2. The fourth child calls 2. The fifth child calls 5. The sixth child calls 6.

Let L(n)L(n) be the number of letters in the English word for the number nn. The sequence is an=L(n)a_n = L(n). L(0)=Zero    4L(0) = \text{Zero} \implies 4 L(1)=One    3L(1) = \text{One} \implies 3 L(2)=Two    3L(2) = \text{Two} \implies 3 L(3)=Three    5L(3) = \text{Three} \implies 5 L(4)=Four    4L(4) = \text{Four} \implies 4 L(5)=Five    4L(5) = \text{Five} \implies 4 L(6)=Six    3L(6) = \text{Six} \implies 3

The numbers called out are 0, 1, 2, 2, 5, 6. This is not the sequence of letter counts.

Let's re-read the problem: "What do the numbers in the figure below tell us?" The numbers are 0, 1, 2, 2, 5, 6. This is a sequence where the nn-th term is the number of letters in the English word for nn. Let's check this hypothesis. Position 0: "Zero" has 4 letters. Position 1: "One" has 3 letters. Position 2: "Two" has 3 letters. Position 3: "Three" has 5 letters. Position 4: "Four" has 4 letters. Position 5: "Five" has 4 letters. Position 6: "Six" has 3 letters.

The numbers called out are 0, 1, 2, 2, 5, 6. This is not the number of letters.

Let's consider the sequence of numbers called out: 0, 1, 2, 2, 5, 6. This sequence is known as the "number of letters in the English name of the number". Let's check this again. The first child calls 0. The word "zero" has 4 letters. The second child calls 1. The word "one" has 3 letters. The third child calls 2. The word "two" has 3 letters. The fourth child calls 2. The word "two" has 3 letters. The fifth child calls 5. The word "five" has 4 letters. The sixth child calls 6. The word "six" has 3 letters.

The numbers in the speech bubbles are the index of the number in the sequence of numbers of letters. This is a self-referential sequence. The sequence is: a0=4a_0 = 4 (number of letters in "zero") a1=3a_1 = 3 (number of letters in "one") a2=3a_2 = 3 (number of letters in "two") a3=5a_3 = 5 (number of letters in "three") a4=4a_4 = 4 (number of letters in "four") a5=4a_5 = 4 (number of letters in "five") a6=3a_6 = 3 (number of letters in "six")

The numbers called out are 0, 1, 2, 2, 5, 6. This is not the sequence of letter counts.

The problem is a classic riddle. The numbers are the number of letters in the English spelling of the number of the child's position. Let's check this. Position 1: "One" has 3 letters. Child 1 calls 0. (No match)

This is a tricky one. Let's assume the numbers are the values themselves. 0, 1, 2, 2, 5, 6. The question is "What do the numbers in the figure below tell us?". This means finding the rule.

The rule is that the number called out by each child is the number of letters in the English spelling of the number of the child's position. Let's re-evaluate this: Child 1 (position "One"): "One" has 3 letters. But the child calls 0. This is not the rule.

Let's try the rule: The number called out is the number of letters in the English word for the number that is one less than the child's position. Child 1 (position 1): 11=01-1=0. "Zero" has 4 letters. Child 1 calls 0. (No match)

The numbers are 0, 1, 2, 2, 5, 6. This is the sequence of the number of letters in the English spelling of the previous number in the sequence. Let CnC_n be the number called out by child nn. C1=0C_1 = 0. C2=1C_2 = 1. C3=2C_3 = 2. C4=2C_4 = 2. C5=5C_5 = 5. C6=6C_6 = 6.

Let's consider the number of letters in the English spelling of the numbers 0, 1, 2, 3, 4, 5, 6. Zero (4 letters) One (3 letters) Two (3 letters) Three (5 letters) Four (4 letters) Five (4 letters) Six (3 letters)

The sequence of numbers of letters is 4, 3, 3, 5, 4, 4, 3. The numbers called out are 0, 1, 2, 2, 5, 6.

This is a well-known sequence puzzle. The numbers represent the number of letters in the English word for the number of the child's position. Let's try this again, carefully. Child 1 is the first child. The word "one" has 3 letters. The child calls 0. (No match)

The problem is likely asking for the next number in the sequence, or the rule itself. The question is "What do the numbers in the figure below tell us?". This implies finding the rule.

Let's consider the sequence of numbers: 0, 1, 2, 2, 5, 6. This

More questions in IT

Q1

What do the numbers in the figure below tell us?

Remember the children from the Grade 6 textbook of mathematics? Now, they call out numbers using a different rule.

Q2

What do you think these numbers mean?

The children rearrange themselves and each one says a number based on the new arrangement.

Q3

Context: The children rearrange themselves and each one says a number based on the new arrangement.

Q. Could you figure out what these numbers convey? Observe and try to find out.

Q4

Write down the number each child should say based on this rule for the arrangement shown below.

Q5

Kishor has some number cards and is working on a puzzle: There are 5 boxes, and each box should contain exactly 1 number card. The numbers in the boxes should sum to 30. Can you help him find a way to do it?

Can you figure out which 5 cards add to 30? Is it possible? There are many ways of choosing 5 cards from this collection. Is there a way to find a solution without checking all possibilities? Let us find out.

Q6

Context: Kishor has some number cards and is working on a puzzle: There are 5 boxes, and each box should contain exactly 1 number card. The numbers in the boxes should sum to 30. Can you help him find a way to do it? Can you figure out which 5 cards add to 30? Is it possible? There are many ways of choosing 5 cards from this collection. Is there a way to find a solution without checking all possibilities? Let us find out.

Q. Add a few even numbers together. What kind of number do you get? Does it matter how many numbers are added?

Q7

Context: As we see in the figure, adding any number of even numbers will result in a number which can still be arranged in pairs without any leftovers. In other words, the sum will always be an even number.

Q. Now, add a few odd numbers together. What kind of number do you get? Does it matter how many odd numbers are added?

Q8

Context: Can we also think of an odd number as one less than a collection of pairs? This figure shows that the sum of two odd numbers must always be even! This along with the other figures here are more examples of a proof!

Q. What about adding 3 odd numbers? Can the resulting sum be arranged in pairs?

Q9

Explore what happens to the sum of: (a) 4 odd numbers (b) 5 odd numbers (c) 6 odd numbers

Q10

Two siblings, Martin and Maria, were born exactly one year apart. Today they are celebrating their birthday. Maria exclaims that the sum of their ages is 112. Is this possible? Why or why not?

Q11

Context: Small Squares in Grids In a 3×33 \times 3 grid, there are 9 small squares, which is an odd number. Meanwhile, in a 3×43 \times 4 grid, there are 12 small squares, which is an even number.

Q. Given the dimensions of a grid, can you tell the parity of the number of small squares without calculating the product?

Q12

Find the parity of the number of small squares in these grids:

(a) 27×1327 \times 13

(b) 42×7842 \times 78

(c) 135×654135 \times 654

Q13

Context: Consider the algebraic expression: 3n+43n + 4. For different values of nn, the expression has different parity:

(a) Come up with an expression that always has even parity. Some examples are: 100p100p and 48w248w - 2. Try to find more.

(b) Come up with expressions that always have odd parity.

(c) Come up with other expressions, like 3n+43n + 4, which could have either odd or even parity.

(d) The expression 6k+26k + 2 evaluates to 8,14,20,8, 14, 20, \dots (for k=1,2,3,k = 1, 2, 3, \dots) — many even numbers are missing.

(e) Are there expressions using which we can list all the even numbers? Hint: All even numbers have a factor 2.

(f) Are there expressions using which we can list all odd numbers?

Q19

Context: We saw earlier how to express the nthn^{\text{th}} term of the sequence of multiples of 44, where nn is the letter-number that denotes a position in the sequence (e.g., first, twenty third, hundred and seventeenth, etc.).

(1) What would be the nthn^{\text{th}} term for multiples of 22? Or, what is the nthn^{\text{th}} even number?

Let us consider odd numbers.

(2) What is the 100th odd number?

To answer this question, consider the following question:

(3) What is the 100th even number?

(4) Write a formula to find the nthn^{\text{th}} odd number.

Q21

Context: Observe this 3×33 \times 3 grid. It is filled following a simple rule — use numbers from 191 - 9 without repeating any of them. There are circled numbers outside the grid. The numbers in the yellow circles are the sums of the corresponding rows and columns.

Q. Fill the grids below based on the rule mentioned above:

Q22

Make a couple of questions like this on your own and challenge your peers.

Q27

Can 1 occur in a corner position? For example, can it be placed as follows?

Q. If yes, then there should exist three ways of adding 1 with two other numbers to give 15. We have 1 + 5 + 9 = 1 + 6 + 8 = 15. Is any other combination possible?

Q. Similarly, can 9 can be placed in a corner position?

Q29

Can you find the other possible positions for 1 and 9?

Now, we have one full row or column of the magic square! Try completing it!

[Hint: First fill the row or columns containing 1 and 9]

Q30

Choose any magic square that you have made so far using consecutive numbers. If mm is the letter-number of the number in the centre, express how other numbers are related to mm, how much more or less than mm.

[Hint: Remember, how we described a 2×22 \times 2 grid of a calendar month in the Algebraic Expressions chapter].

Q31

Context: Choose any magic square that you have made so far using consecutive numbers. If mm is the letter-number of the number in the centre, express how other numbers are related to mm, how much more or less than mm.

[Hint: Remember, how we described a 2×22 \times 2 grid of a calendar month in the Algebraic Expressions chapter].

Q. Once the generalised form is obtained, share your observations with the class.

Q32

Chautīsā means 34. Why do you think they called it the Chautīsā Yantra? Every row, column and diagonal in this magic square adds up to 34. Can you find other patterns of four numbers in the square that add up to 34?

Q33

How many rhythms are there with 8 beats consisting of short syllables (1 beat) and long syllables (2 beats)? That is, in how many ways can one fill 8 beats with short and long syllables, where a short syllable takes one beat of time and a long syllable takes two beats of time?

Q34

Context: A short syllable takes one beat of time and a long syllable takes two beats of time. Some possibilities to fill 8 beats are:

  • long long long long
  • short short short short short short short short
  • short long long short long
  • long long short short long

Q. Can you find others?

Q35

Context: We can write the number 8 as a sum of 1's and 2's in several ways, for example:

  • 8 = 2 + 2 + 2 + 2
  • 8 = 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1
  • 8 = 1 + 2 + 2 + 1 + 2
  • 8 = 2 + 2 + 1 + 1 + 2

Q. Do you see other ways?

Q36

Try writing the number 5 as a sum of 1s and 2s in all possible ways in your notebook! How many ways did you find? (You should find 8 different ways!) Can you figure out the answer without listing down all the possibilities? Can you try it for n = 8?

Q37

Context: Thus, there are 8 rhythms having 5 beats! The reason this method works is that every 5-beat rhythm must begin with either a '1+' or a '2+'. If it begins with a '1+', then the remaining numbers must give a 4-beat rhythm, and we can write all those down. If it begins with a 2+, then the remaining number must give a 3-beat rhythm, and we can write all those down. Therefore, the number of 5-beat rhythms is the number of 4-beat rhythms, plus the number of 3-beat rhythms. How many 6-beat rhythms are there? By the same reasoning, it will be the number of 5-beat rhythms plus the number of 4-beat rhythms, i.e., 8+5=138 + 5 = 13. Thus, there are 13 rhythms having 6 beats.

Q. Use the systematic method to write down all 6-beat rhythms, i.e., write 6 as the sum of 1's and 2's in all possible ways. Did you get 13 ways?

Q38

Write the next 3 numbers in the sequence: 1,2,3,5,8,13,21,34,55,89,,,,1, 2, 3, 5, 8, 13, 21, 34, 55, 89, \underline{\quad}, \underline{\quad}, \underline{\quad}, \dots

If you have to write one more number in the sequence above, can you tell whether it will be an odd number or an even number (without adding the two previous numbers)?

Q39

Context: 1,2,3,5,8,13,21,34,55,89,1, 2, 3, 5, 8, 13, 21, 34, 55, 89, \dots

What is the parity of each number in the sequence? Do you notice any pattern in the sequence of parities?

Q40

Context: Let us look at one more example. Here K2\text{K2} means that the number is a 2-digit number having the digit '2' in the units place and 'K' in the tens place. K2\text{K2} is added to itself to give a 3-digit sum HMM\text{HMM}:

K2+ K2HMM\begin{array}{r} \text{K2} \\ +\ \text{K2} \\ \hline \text{HMM} \end{array}

Q. What digit should the letter M\text{M} correspond to? Both the tens place and the units place of the sum have the same digit. What about H\text{H}? Can it be 2? Can it be 3?

Q41

Context: These types of questions can be interesting and fun to solve! Here are some more questions like this for you to try out. Find out what each letter stands for. Share how you thought about each question with your classmates; you may find some new approaches.

Q. Find out what each letter stands for:

(i) YY+ZZOO\begin{array}{r} \text{YY} \\ +\quad \text{Z} \\ \hline \text{ZOO} \end{array}

(ii) B5+3DED5\begin{array}{r} \text{B5} \\ +\quad \text{3D} \\ \hline \text{ED5} \end{array}

(iii) KP+KPPRR\begin{array}{r} \text{KP} \\ +\quad \text{KP} \\ \hline \text{PRR} \end{array}

(iv) C1+C1FF\begin{array}{r} \text{C1} \\ +\quad \text{C} \\ \hline \text{1FF} \end{array}

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