Question

A certain sum of money amounts to rs.2,500 in a span of 5 years and further to rs.3000 in a span of 7 years at simple interest

Answer 1

let principal is x
and interest rates y
then
x(1+5y/100)=2500
or x(100+5y)=250000
or x=250000/(100+5y)..... ......(1)
again
x(1+7y/100)=3000
or x=300000/(100+7y)
then
300000/(100+7y)=250000/(100+5y)
or 30(100+5y)=25(100+7y)
or 3000+150y=2500+175y
or 25y=500
or y=20................(ans)
putting the value of y in (1)
x=250000/(100+7*20)
or x=250000/240
or x=25*125/3
or x=25*41.67
or x=1041.75............(ans)