A mobile phone is bought for ₹ 10,000. Its value decreases by ₹ 800 every year. Class 9
A mobile phone is bought for ₹ 10,000. Its value decreases by ₹ 800 every year. Class 9
Question 1.
A mobile phone is bought for ₹ 10,000. Its value decreases by ₹ 800 every year. Class 9
i. Find the value of the phone after 3 years.
ii. Make a table of values for t varying from 0 to 8 years and show how the value of the phone, v, depreciates with time.
iii. Find an expression that relates v and t, and explain why it represents linear decay.
Solution:
Initial value of the mobile phone = ₹ 10,000
Decrease in value each year = ₹ 800
i. Number of years (t) = 3
Value of the phone after t years
= Initial value - (Decrease in value per year × t)
∴ Value of the phone after 3 years
= 10000 - (800 × 3)
= 10000 - 2400
= ₹ 7600
∴ The value of the phone after 3 years is ₹ 7600.
ii.
| Year (t) | Value (v) (₹) |
| 0 | 10,000 |
| 1 | 10,000 - 800 × 1 = 9,200 |
| 2 | 10,000 - 800 × 2 = 8,400 |
| 3 | 10,000 - 800 × 3 = 7,600 |
| 4 | 10,000 - 800 × 4 = 6,800 |
| 5 | 10,000 - 800 × 5 = 6,000 |
| 6 | 10,000 - 800 × 6 = 5,200 |
| 7 | 10,000 - 800 × 7 = 4,400 |
| 8 | 10,000 - 800 × 8 = 3,600 |
iii. The linear expression that relates the value of the phone (v) and the number of years (t) is v = 10000 - 800t
Every year the value of the phone decreases by a fixed amount ₹800.
∴ It represents linear decay.