Question

an investor received $1400 interest per annum from a sum of money, with part of it invested at 10% and the remainder at 7% simple interest. This investor found that if she interchanged the amounts she had invested she could increase her return by $90 per annum. Calculate the total amount invested.

Answer 1

Explanation:

let x be one part of the money invested.

let y be the other part of the money invested.

x *(10/100) -- amount on 10% of interest per annum

y*(7/100)- amount invested on 7% of interest per annum

x *(10/100) + y*(7/100) =1400

on simplifying it

10x +7y =140000 --(1)

On interchanging the interest rate on x amount and y amount of the investor

x *(7/100) + y*(10/100) =1490

7x +10y =149000-(2)

on solving equation (1) and (2) we get

70x +49y =980000

70x + 100y =1490000

-51y= -510000

y=10000

and x=7000

So our total amount invested is 17000