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Math Help - Another investment question

  1. #1
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    Another investment question

    Susan places $4900 in three investments at rates of 9%, 10.8% and 16.2% per annum, respectively. The total income after one year is $ 640.80 . If the amount placed in the third investment is $900 more than the amount placed in the second, find the amount of each investment.




    and also...


    The admission fee at an amusement park is $ 1.50 for children and $ 4.00 for adults. On a certain day, 291 people entered the park, and the admission fees collected totaled $824 . How many children and how many adults were admitted?
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  2. #2
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    Quote Originally Posted by asugirl87 View Post
    Susan places $4900 in three investments at rates of 9%, 10.8% and 16.2% per annum, respectively. The total income after one year is $ 640.80 . If the amount placed in the third investment is $900 more than the amount placed in the second, find the amount of each investment.
    I will help you on the construction on this problem only so that you will have a chance to learn on your own. Working problems like this by yourself is important to the understanding of problem solving.

    So we have three investments, lets say
    x is the investment for the rate of 9%
    y is the investment for the rate of 10.8%
    z is the investment for the rate of 16.2%

    Since Susan invests $4900 we know that

    1) x + y + z = 4900

    Since the total interest of that year is 640.80, we also know that the sum of the generated interest from each investment totals this number. So

    2) .09x + .108y + .162z = 640.80

    Since we know the amount placed in the third investment is $900 more than the amount placed in the second (I'll assume respectively from lower to higher interest rate), then

    3) y = z + 900

    Using 1,2,3 solve for the system of linear equations.
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