21.
A sum of money trebles itself in 15 years 6 months. In how many years would it double itself?
• A.
6 years 3 months
• C.
8 years 3 months
• B.
7 years 9 months
• D.
9 years 6 months
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Explanation :

 Let sum = x. Then, S.I. = 2x, Time = 15 1 years = 31 years. 2 2

Rate =
 100 x 2x x x 31 2
% = 400 %
31

 Now, sum = x, S.I. = x, Rate = 400 % 31

Time = 100 x x = 31  years = 7 years 9 months.
 x x 400 31
4

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22.
A six years NSC certificate was purchased for Rs. 500 with Rs. 1000 being the maturity value. Find the rate of S.I.
• A.
16%
•  C.16 4 % 3
•  B.16 2 % 3
•  D.15 2 % 3
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Explanation :

P = Rs. 500; SI = 500; N = 6 years.

 R = 100 x I = 100 x 500 = 16 2 % PT 500 x 6 3

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23.
Ravi borrowed Rs. 2500 from A and B. For A, he paid 5% and for B he paid 7%. The total interest paid by him is Rs. 160. Find the amount borrowed from A.
• A.
750
• C.
1000
• B.
900
• D.
1500
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Explanation :

Let the amount borrowed from A be Rs. x.

 Int. paid = x x 5 = 5x 100 100

 Int. paid to B = (2500 - x)7 100

 17500 - 7x 100

Total Interest = 160

 5x + 17500 - 7x = 160 100 100

-2x + 17500 = 16000

-2x = -1500

 x = 750

Amount borrowed from A = Rs. 750

Amount borrowed from B = 2500 - 750

 = Rs. 1750

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24.
Find the rate of C.I at which Rs. 1000 becomes Rs. 5000 in 4 years
• A.
10%
• C.
50%
• B.
15%
• D.
30%
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Explanation :

P = 1000 Rs. A = 5000, n = 4

The formula is A = p

1 +
 r 100
n

5000 = 1000 1 +
 r 100
4

1+
 r 100
4 =
 5000 =5 1000

 1 + r = 1.50 100

 r = 1.50 - 1 = .50 100

 r = .5 x 100 = 50%

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25.
The simple interest on Rs. 500 at 6% per annum from May 3rd to July 15th in the same year is
• A.
Rs. 9
• C.
Rs. 4
• B.
Rs. 6
• D.
None of these
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Explanation :

Time from May 3rd to July 15th = 28 days of May + 30 days of June and 15 days of July

 = 73 days = 73 years, i.e. 1 years 365 5

 I =

 =
 500 x 6 x 1 5

P x R x T  = Rs. 6
100 100

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