51.
A sum of money doubles in 8 years. In how many years, it will treble at S.I.
• A.
4
• C.
12
• B.
8
• D.
16
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Explanation :

Here P is the same

A simple ratio will give the Time

 8 = 1 T 2

 T = 16 years

i.e., In 16 years, the amount will treble

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52.
A sum was put a simple interest at a certain rate for 2 years. Had it been put at 3% higher rate, it would have fetched Rs. 72 more. The sum is:
• A.
Rs. 1200
• C.
Rs. 1600
• B.
Rs. 1500
• D.
Rs. 1800
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Explanation :

 Let the sum be Rs. x and original rate be R%. Then, x x (R + 3) x 2 - x x R x 2 = 72 100 100

 2Rx + 6x - 2Rx = 7200

 x = 1200.

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53.
The interest on a certain deposit at 4.5% per annum is Rs. 202.50 in one year. How much will the additional interest in one year be on the same deposit at 5% per annum?
• A.
Rs. 20.25
• C.
Rs. 25
• B.
Rs. 22.50
• D.
Rs. 42.75
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Explanation :

S.I. = Rs. 202.50, R = 4.5%, T = 1 year.

 Principal = Rs. 100 x 202.50 = Rs. 4500 4.5 x 1

Now, P = Rs. 4500, R = 5%, T = 1 year.

 S.I. = Rs. 4500 x 5 x 1 = Rs. 225 100

 Difference in interest = Rs. (225 - 202.50) = Rs. 22.50.

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54.
A sum of money amounts to Rs. 9800 after 5 years and Rs. 12005 after 8 years at the same rate of simple interest. The rate of interest per annum is :
• A.
5%
• C.
12%
• B.
8%
• D.
15%
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Explanation :

S.I. for 3 years = Rs. (12005 - 9800) = Rs. 2205.

S.I. for 5 years = Rs.
 2205 x 5 3
= Rs. 3675.

 Principal = Rs. (9800 - 3675) = Rs. 6125

Hence, rate =

 100 x 3675 6125 x 5
% = 12%

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55.
A man invests a certain sum of money at 6% per annum simple interest and another sum at 7% per annum simple interest. His income from interest after 2 years was Rs. 354. One-forth of the first sum is equal to one-fifth of the second sum. The total sum invested was :
• A.
Rs. 2600
• C.
Rs. 2880
• B.
Rs. 2700
• D.
Rs. 2900
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Explanation :

Let the sums be x and y.

 x x 6 x 2 + y x 7 x 2 = 354 or 6x + 7y = 17700. ...(i) 100 100

 Also, x = y or 5x - 4y = 0 ...(ii) 4 5

Solving (i) and (ii), we get : x = 1200 and y = 1500.

 Total sum = Rs. 2700.

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