Find the Sum.

The compound interest on a certain sum for 2 year is Rs 105 and simple interest is Rs 100. Find the sum.

  1. Rs. 300
  2.  Rs. 500
  3.  Rs. 400
  4.  Rs. 600
Desire Adnan Default Asked on 4th August 2015 in Maths.
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1 Answer(s)

Answer: (2) Rs.500
Explanation:-
Let the principal be Rs.X
Given-
Time = 2 years, Compound Interest = Rs.105   & Simple  Interest = Rs.100

Formula-
The ratio of Compound Interest & Simple Interest same sum at R %  for N  years .
Then, C I /S I = R /N x 100 + 1

Then,  105 / 100 = R / 2 x 100 + 1
21 / 20 = R/ 200 + 1
21 / 20 = (R + 200) / 200
21 x 200 = (R + 200) x 20
4200 = 20 R + 4000
20 R = 4200 – 4000
20 R = 200
R = 200/20
R = 10 %

Formula-
Simple Interest = P x R x T/100
Where, P = principal , R = rate, & T = time.

Then, 100 = X x 10 x 2 /100
100 = 20 X /100
20 X = 100 x 100
20 X = 10000
X = 10000/20
X = 1000/2
X = Rs.500

Then, the sum is Rs.500
Hence, the answer is (2) Rs.500.

Anurag Mishra Professor Answered on 6th August 2015.
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