  Selina solutions

Q13) A sum amounts to Rs. 2,652 in 6 years at 5% p.a. simple interest.

Find :

(i) the sum

(ii) the time in which the same sum will double itself at the same rate of interest.

Solution:

(i) In first case, Let principal (P) = Rs. 100

Rate ( r ) = 5% p.a , Time (T) = 6 years

∴ SI = \frac{PRT}{100}=\frac{100\times6\times5}{100}=Rs.30

And, amount = Rs. 100 + 30 = Rs. 130

If amount is Rs. 130 , then principal = Rs. 100

And, if amount is Rs. 2652 then principal

=\frac{100\times2652}{130}=Rs.2040

(ii)In second case, let sum (P) = Rs. 100

Amount (A) = 100 x 2 = Rs. 200

SI = A - P = 200 - 100 = 100 Rs.

Rate = 5% p.a

Time = \frac{SI\times100}{P\times R}=\frac{100\times100}{100\times5}=20\ years

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