Question

At what percentage of rate per annum simple interest,will a certain sum of money becomes double in 10 years ? A. 20% B. 10% . C. 15% . D. 18% .

Answer 1

Let the percentage of rate per annum = r
Initial amount = P
Final amount = 2P
We know, A = P + S.I and S.I = P × r × T/100 , here T is time .
e.g., 2P = P + P × r × T/100
Given, T = 10 yrs
∴ 2P = P + P × r × 10/100
P = P × r/10
r = 10%

Hence answr is option (C)

Answer 2

Solution:-

》let principal amount is( p)= 100rupees

》intrest rate (r) = r

》time (n) = 10years

by formula

》s.i = (p×r×n)/100

》s.i = (100×r×10)/100

》s.i = 10r

》total money (A)= principal amount (p)+s.i
》
A = 100+10r

》 A = 10(10+r)..........(1)

》Acourding to quetion:-

》money becomes double in 10 years

then
we have,

》A = 2×p

》10(10+r) = 2×100

》 r = 20-10

》 ( r = 10%) ans

》your right option is( B) 10%