Question

A sum of money lent out at simple interest amounts to rs 720 after 2 years and to rs 1020 after a further period of 5 years find the sum

Answer 1

Answer:

Let the sum be x and interest rate be y. So x+2yx=720 and x+7yx=1020 so substracting first from second gives 5yx=300 y=60/x.now putting this in first gives x(1+120/x)=720 or x+120=720 or x=600 and y=60/600=.1 or 10%per year.