Question

at what rate per cent will a sum of 640 be compounded to 774.40 in two year

Answer 1

We know that A = P(1+r/100)^n
 
                      774.40 = 640(1+r/100)^2

                      1.21 = (1+r/100)^2

                      1.1 = 1+r/100

                      0.1 = r/100

                       r = 10%.


Hope this helps!

Answer 2

The rate of interest was 10%
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