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13 March, 15:29

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.

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  1. 13 March, 16:49
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    Step-by-step 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
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