11.
The simple interest and the true discount on a certain sum for a given time and at a given rate are Rs. 85 and Rs. 80 respectively. The sum is:
• A.
Rs. 1800
• C.
Rs. 1360
• B.
Rs. 1450
• D.
Rs. 6800
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Explanation :
Sum =
 S.I x T.D. (S.I) - (T.D.)
=
 85 x 80 (85 - 80)
= Rs. 1360
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12.
Find the true discount on Rs. 39.69 due in 2 years reckoning compound interest at 5%
• A.
Rs. 3.69
• C.
Rs. 5.69
• B.
Rs. 5
• D.
Rs. 4.69
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Explanation :

 P.W. =
39.69
1 x
 5 100
2

 3969 x 100 x 100 100 x 105 x 105

 = Rs. 36
True discount = Rs. 39.69 – 36 = Rs. 3.69
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13.
If the true discount on a sum due 2 years hence at 14% per annum be Rs. 168, the sum due is:
• A.
Rs. 768
• C.
Rs. 1960
• B.
Rs. 968
• D.
Rs. 2400
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Explanation :
P.W. =
 100 x T.D. R x T
=
 100 x 168 14 x 2
= 600.
Sum = (P.W. + T.D.) = Rs. (600 + 168) = Rs. 768.
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14.
The true discount on a certain sum of money due after 2
 1 2
years at 6% per annum is less
than the simple interest on the same sum for the same time by Rs. 81. Find the sum -
• A.
Rs. 4140
• C.
Rs. 4150
• B.
Rs. 4240
• D.
Rs. 4250
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Explanation :
Req. amount =
81 x   100 + 6 x
 5 2
x 100
6 x
 5 2
2

 8100 x 115 225

 = Rs. 4140

 Here, S.I. - T.D. = Rs. 81
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15.
Find the present worth of a bill of Rs. 2420 due 2 years hence at 10% compound interest. Also find the true discount -
• A.
Rs. 2000, Rs. 420
• C.
Rs. 2100, Rs. 460
• B.
Rs. 2200, Rs. 520
• D.
None of these
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Explanation :
Here sum is put on compound interest,

 P.W. =
A
1 +
 r 100
n
 =
2420
1 +
 10 100
2

 2420 x 100 121

 = Rs. 2000
T.D.  = P.W. - P
True discount = 2420 – 2000 = Rs. 420.
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