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CBSE Class 7 Answered

Lily borrowed rupees 4000 from a friend at 5% for some years and return a sum of rupees 5200 by what time did he returned it
Asked by Cdpopiprali0 | 28 Jan, 2019, 08:04: PM
answered-by-expert Expert Answer
TYpe of interest , whether it is simple interest or interest compounded annualy, is not mentioned.
Answer is worked out for both the types.
 
Simple interest :-
 
Simple Interest I = (pnR)/100 , where p is principle amount, n is number of years, R is rate of interest
 
I = Rs.5200-Rs.4000 = Rs.1200
 
hence   (4000×n×5)/100 = 1200  or 200n = 1200  or n = 6 years.
 
Compound Interest :-
 
Amount A after n years is given by,    P[ 1 +(r/100) ]n = A
 
4000×[ 1+(5/100) ]n = 5200  or  ( 1.05 )n = 5200/4000 = 1.3
 
hence n×log(1.05) = log(1.3)
 
By solving the above eqn., we get n ≈ 5.4 years ≈ 5 years 5 months
Answered by Thiyagarajan K | 28 Jan, 2019, 08:45: PM

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