Page 99 - Maths Skills - 7

Comparing Quantities 97

Example 3: A sum of ` 4000 is lent for 5 years at the rate of 15% per annum. Find the simple interest.

Solution: Here, P = ` 4000, R = 15% per annum and T = 5 years.

Since, S.I. = P × R × T = ` 4000 × 15 × 5
100 100
S.I. = ` 3000
Hence, ` 4000 for 5 years at 15% will earn an interest of ` 3000.

Example 4: In how many years will ` 1500 amount to ` 2100 at 6% per annum?
Solution: Here, P = ` 1500, A = ` 2100 and R = 6% per annum.
We know that, A = P + S.I.

\ S.I. = A – P = ` 2100 – ` 1500 = ` 600
and S.I. = P × R × T
100
2
\ T = S.I. × 100 = 600 × 100 years = 6 years.
P × R 1500 × 6 3
2
Hence, ` 1500 will amount to ` 2100 at 6% in 6 years.
3
Example 5: A man borrowed ` 1500 at 6% per annum and promised to return it after 146 days along with the
interest. Find the amount to be paid at the end of 146 days.

Solution: Here, P = ` 1500, R = 6% per annum and T = 146 days = 146 years.
365
Since S.I. = P × R × T = 1500 × 6 × 146 = ` 36
100 100 × 365
Now, Amount (A) = P + S.I. = ` 1500 + ` 36 = ` 1536
Hence, the amount to be paid at the end of 146 days is ` 1536.

1 1
Example 6: Find the principal which will earn an interest of ` 325 at 4 % per annum in 8 years.
3 3
1 13 1 25
Solution: Here, S.I. = ` 325, R = 4 % = % and T = 8 years = years.
3 3 3 3
We know that, S.I. = P × R × T
100

\ P = S.I. × 100 = ` 325 × 100 × 3 × 3 = ` 900
R × T 13 × 25
1
1
Hence, ` 900 will earn an interest of ` 325 at 4 % in 8 years.
3 3

Exercise 5.6

1. At what rate will ` 3000 amount to ` 3360 in 3 years?
2. Amit deposited ` 5000 in a bank which pays 8% per annum interest on deposits. How much interest will
he get at the end of 4 years?
3. Find the interest on ` 1250 at 18% per annum for a period of 2 years 4 months.

4. In how many years will ` 750 amount to ` 900 at 4% per annum?
5. Find the interest on ` 1600 for 36 months at 4% per annum.