Question

A sum of money amounts to 52,080 in 2years and to 77,280 in 7 years,at simple intrest.find the sum and rate percentage of intrest

Answer 1

simple interest formula is  

Value = principle x ( 1 + (( rate of interest x no. of years) /100) )

here, principle is given as sum

1st condition,

             Value(V1)          = 52,080

             no. of years(n1) = 2

therefore,             52080 = sum * ( 1 + (2r/100)  )                        ..............(1)

2nd condition

           V2 = 77280     ,          n2 = 7

therefore value,             77280 = sum *  ( 1 + (7r/100)  )                ................(2)

On solving both the conditions, we get  

                      interest r ≈ 12%

and                 Sum  =  42000