the difference between the compound interest and simple on a sum of..., Compound Interest, General Mathematics

Question:The difference between the compound interest and the simple interest on a sum of money for `2` years at `12 1/2%`per annum is Rs.`150`.The sum is :

A `Rs. 9000` 
B `Rs. 9200` 
C `Rs. 9500` 
D `Rs. 9600`

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+ AnswerD

+ ExplanationLet the sum be  Rs.x. Then,

`C.I = x (1 + 25/(2 xx 100))^2 - x`

`= (9/8 xx 9/8) x - x`

`= (17x)/64`.

`S.I = (x xx 25/2 xx 2 xx 1/100)`

`= x/4`

`(C.I.) - (S.I.) = ((17x)/64 - x/4)`

`= x/64`

`:. x/64 = 150`

`or x = 9600`.

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