Question

At what rate percent will a sum of rs 640 be compounded to rs 774.40 in two years?

Answer 1

774.40=640(1+r/100)²
774.40/640=(1+r/100)²
(1.1)²=(1+r/100)²
1.1=1+r/100
r/100=1.1-1
r/100=0.1
r=0.1*100
r=10%pa

Answer 2

Given - Principal, amount, time

Find - Rate percent

Solution - Rate percent is 10%.

Amount = Principal (1+r/100)^n

774.4 = 640 (1+r/100)²

Performing division

1.21 = (1+r/100)²

Taking square root

1 + r/100 = ✓1.21

1 + r/100 = 1.1

Performing subtraction

r/100 = 1.1 - 1

r/100 = 0.1

Performing multiplication

r = 0.1*100

r = 10%

So, the rate of interest is 10%.