Page 125 - ICSE Math 7

P × R × T 700 × 21 × 6
S.I. = 100 ⇒ S.I. = 100 × 2

⇒ S.I. = ` 441

A = P + S.I. = ` 700 + ` 441 = ` 1,141
Example 9: Ria and Tia invest ` 5,000 and ` 8,000 respectively at the same rate of interest per
annum. If at the end of 4 years, Tia gets ` 500 more interest than Ria, find the rate of
interest.

P × R × T
Solution: For Ria, S.I. =
100
5,000 × R × 4
⇒ S.I. = = ` 200R
100
P × R × T
For Tia, S.I. =
100
8,000 × R × 4
⇒ S.I. = = ` 320R
100
Since Tia gets ` 500 more than Ria, therefore

320R – 200R = 500
⇒ 120R = 500
1
⇒ R = 4 % per annum
6
Alternatively,
Tia invests ` 3,000 (` 8,000 – ` 5,000) more than Ria.

\ Interest on ` 3,000 for 4 years = ` 500
3,000 × R × 4
⇒ 100 = 500

1
⇒ R = 4 % per annum
6
Example 10: Find the interest paid on ` 9,600 from July 26 to October Maths Info
7 at the rate of 7% per annum.
Solution: P = ` 9,600, R = 7% per annum To find the number of days,
starting day is not included
July August September October but the last day is included.

T = 5 days + 31 days + 30 days + 7 days For example, to calculate
73 1 number of days from 18 August
= 73 days = = year to 5 September, we start count
365 5 from 19 August to 5 September
P × R × T 9,600 × 7 × 1 so, there are 18 days.
S.I. = = = ` 134.40
100 100 × 5

EXERCISE

1. Find the simple interest and amount on:
(a) ` 250 for 3 years at the rate of 6% p.a. (b) ` 900 for 2 years at the rate of 11% p.a.
(c) ` 1,800 for 2 years at the rate of 7% p.a. (d) ` 800 for 3 years at the rate of 2% per annum

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