# Compound Interest Quizzes for LIC assistant 2021, CET and SBI Clerk Pre 2021 at Smartkeeda

Important for :
1
The SI on a certain sum of money for 3 yr at 8% pa is half the CI on Rs. 8000 for 2 yr at 10% pa. Find the sum placed on simple interest?
» Explain it
A
Applyng the net% effect formula, we get

 = 10 + 10 + 10 × 10 = 21% 100

Now, 21% of 8000 = 1680

 Sum of SI is half of CI = 1680 = 840 2

 ∴   Sum = 840 × 100 = ₹ 3500 3 × 8

Hence, option A is correct.

2
What is the CI accrued on an amount of Rs. 12000 at the rate of 9% per annum at the end of 2 years?
» Explain it
B
Method I :

P = ₹ 12000; R = 9%; n = 2 years

 CI = P ( 1 + R ) n – P 100

 CI = 12000 ( 1 + 9 ) 2 – 12000 100

 = 12000 × 109 × 109 – 12000 100 100

= 14257.20 – 12000 = ₹ 2257.20

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Method II :

To solve this question, we can apply the net% effect formula

 Net% effect = ( x + y + xy ) % 100

Here, x = y = 9%         (because rate of interest is same for both the years)

By the net% effect, we get effective rate of interest

 = ( 9 + 9 + 9 × 9 ) % = 18.81% 100

Therefore, 18.81% of 12000  =  ₹ 2257.20

Hence, option B is correct.

3
Sachin had ₹ 23,000. He invested some amount in scheme A at SI at 20% and the remaining amount in scheme B at CI at 10%. If Sahil got the same amount from both of them at the end of one year, how much (in ₹) did he invest in scheme B ?
» Explain it
D
Let the amount invested in scheme B is ₹ x.

∴  Amount invested in scheme A be ₹ (23000 – x).

According to the question,

 (23000 – x) + (23000 – x) × 20 × 1 = x + x ( 1 + 10 ) 1 – x 100 100

 ⇒  (23000 – x) × 6 = 11x 5 10

⇒  11x = 276000 – 12x

⇒  23x = 276000

⇒  x = 12000

Hence, option D is correct.

4
The difference between simple interest and compound interest on a certain sum of money for 2 years at 5% per annum is ₹ 100. Find the sum.
» Explain it
D
Method I :

To solve this question, we can apply a short trick approach

 Sum = Difference × 1002 r2

Given, Difference = ₹ 100,  r = 5%

By the short trick approach, we get

 Sum = 100 × 1002 = ₹ 40000 52

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Method II :

We can solve it by the net% formula,

Rate % of SI for 2 yr at 5% pa = 5 × 2 = 10%

Rate % of CI for 2 yr at 5%,

 5 + 5 + 5 × 5 = 10.25% 100

% rate difference of CI and SI = 10.25% – 10% = 0.25%

Let the sum be ₹ x, then

0.25% of x = 100

 x = 100 × 100 = ₹ 40000 0.25

Hence, option D is correct.

5
What will be the compound interest on a sum of ₹ 9000 at compound interest compounded annually at 8% per annum in two years ?
» Explain it
B
Given, P = ₹ 9000; R = 8%; n = 2 years

 CI = P ( 1 + R ) n – P 100

 = 9000 ( 1 + 8 ) 2 – 9000 100

 = 9000 ( 27 ) 2 – 9000 25

 = 9000 ( 729 – 1 ) 625

 = 9000 × 104 = ₹ 1497.6 625

Hence, option B is correct.