Page 123 - ICSE Math 7

A = P + S.I.

\ A = ` 6,600 + ` 2,640 = ` 9,240
1
Example 3: Mr Mishra took a loan from a bank for 2 years at the rate of 7 % per annum. He had
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to pay ` 2,025 as interest at the time of repaying the loan. Find the amount of loan he
took from the bank.
1 15
Solution: T = 2 years, R = 7 % = % and S.I. = ` 2,025
2 2
P × R × T
S.I. =
100
P × 15 × 2
2,025 =
100 × 2

⇒ P = 2,025 × 100 = ` 13,500
15

Example 4: Find the rate of interest at which a sum of money will triple itself in 4 years.
Solution: Let the principal be ` 100. As money will triple itself in 4 years, the amount is ` 300
after 4 years.
S.I. = A – P = ` 300 – ` 100 = ` 200
P × R × T
S.I. =
100
100 × R × 4
\ 200 =
100
200
⇒ R = = 50% per annum
4
3
Example 5: In how much time will the interest be of the principal at the rate of 4% per annum?
5
Solution: Let the principal be ` x.
3 3x
\ S.I. = of ` x = `
5 5
P × R × T
S.I. = 100

3x x × 4 × T
\ =
5 100
25 × 3
⇒ T = 5 = 15 years

Example 6: Rohit deposited ` 1,000 in a fixed deposit scheme in a bank which gives interest at the
rate of 10% per annum. At maturity, he received ` 2,500 from the bank. Find the term
of the fixed deposit scheme.
Solution: P = ` 1,000, A = ` 2,500 and R = 10% per annum
S.I. = A – P = ` 2,500 – ` 1,000 = ` 1,500
P × R × T
S.I. = 100

1,000 × 10 × T
⇒ 1,500 = ⇒ T = 15 years
100

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