Introduction to Linear Polynomials | Exercise 2.4

Question 3

The initial population of a village is 750. Every year, 50 people move from a nearby city to the village.

(i) Find the population of the village after 6 years.

(ii) Make a table of values for tt varying from 0 to 10 years and show how the population, PP, increases every year.

(iii) Find an expression that relates PP and tt, and explain why it represents linear growth.

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Solution

The village population grows by a fixed number of people each year.

Step 1 — Calculate population after 6 years

We start with the initial population. People move in every year. We need to find the total increase. Then, we add it to the initial population.

Initial population=750\text{Initial population} = 750

People moving in per year=50\text{People moving in per year} = 50

Number of years=6\text{Number of years} = 6

Total people moved in=50×6\text{Total people moved in} = 50 \times 6

=300= 300

Population after 6 years=750+300\text{Population after 6 years} = 750 + 300

1050 people\boxed{1050 \text{ people}}

Step 2 — Create the population table

Let's make a table. We will show population for each year. The population starts at 750. It increases by 50 each year.

| t (years) | P (population) | |---|---| | 0 | 750 | | 1 | 800 | | 2 | 850 | | 3 | 900 | | 4 | 950 | | 5 | 1000 | | 6 | 1050 | | 7 | 1100 | | 8 | 1150 | | 9 | 1200 | | 10 | 1250 |

Step 3 — Find the expression and explain linear growth

Let PP be the population. Let tt be the number of years. The initial population is 750. The population increases by 50 each year. So, after tt years, the increase is 50×t50 \times t. We add this to the initial population.

P=Initial population+(Annual increase×t)P = \text{Initial population} + (\text{Annual increase} \times t)

P=750+(50×t)P = 750 + (50 \times t)

P=750+50t\boxed{P = 750 + 50t}

This represents linear growth. The population increases by a constant amount. It increases by 50 people every year. This constant rate of change defines linear growth.

Answer

(i) The population of the village after 6 years is 1050. (ii) | t (years) | P (population) | |---|---| | 0 | 750 | | 1 | 800 | | 2 | 850 | | 3 | 900 | | 4 | 950 | | 5 | 1000 | | 6 | 1050 | | 7 | 1100 | | 8 | 1150 | | 9 | 1200 | | 10 | 1250 | (iii) The expression relating PP and tt is P=750+50tP = 750 + 50t. This represents linear growth because the population increases by a constant number (50 people) every year.

More questions in Exercise 2.4

Q1

Suppose a plant has height 1.75 feet and it grows by 0.5 feet each month.

(i) Find the height after 7 months.

(ii) Make a table of values for tt varying from 0 to 10 months and show how the height, hh, increases every month.

(iii) Find an expression that relates hh and tt, and explain why it represents linear growth.

Q2

A mobile phone is bought for ₹10,000. Its value decreases by ₹800 every year.

(i) Find the value of the phone after 3 years.

(ii) Make a table of values for tt varying from 0 to 8 years and show how the value of the phone, vv, depreciates with time.

(iii) Find an expression that relates vv and tt, and explain why it represents linear decay.

Q3

The initial population of a village is 750. Every year, 50 people move from a nearby city to the village.

(i) Find the population of the village after 6 years.

(ii) Make a table of values for tt varying from 0 to 10 years and show how the population, PP, increases every year.

(iii) Find an expression that relates PP and tt, and explain why it represents linear growth.

Q4

A telecom company charges ₹600 for a certain recharge scheme. This prepaid balance is reduced by ₹15 each day after the recharge.

(i) Write an equation that models the remaining balance b(x)b(x) after using the scheme for xx days. Explain why it represents linear decay.

(ii) After how many days will the balance run out?

(iii) Make a table of values for xx varying from 1 to 10 days and show how the balance b(x)b(x) reduces with time.

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