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

Directions: Read the following questions carefully and answer them:
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

______________________________________________

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

________________________________________________

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.