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Question
Mohan invested a certain sum at compound interest, compounded annually. If the interests for two successive years were Rs 600 and Rs 648, calculate the rate of interest and the sum invested.
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Solution
For the second year:
A=Rs 648 ; P=Rs 600 ; n=1 ; r = ?
`therefore "A" = "P" (1 + "r"/100)^"n"`
`⇒ 648 = 600 (1 + "r"/100)^1`
⇒ 648 = 600 + 6r
⇒ 6r = 48
⇒ r = 8
Hence, rate of interest = 8 %
For the first year:
I=Rs 600 ; r=8 % ; n=1 ; P = ?
`"I" =("P" xx "r" xx "n")/100`
Rs 600 = Rs `("P" xx 8 xx 1)/100`
P = Rs `60000/8`
P = Rs 7,500
The sum invested= Rs 7,500.
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