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22 June, 16:14

What times what equals 30 but add to get 40?

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Answers (2)
  1. 22 June, 16:15
    0
    Lets call those two unknown numbers a, b and write the info in the problem as equations:

    a*b = 30

    a + b = 40

    lets solve for a in the second equation and substitute in the first:

    a + b = 40

    a = 40 - b

    therefore:

    a*b = 30

    (40 - b) b = 30

    40b - b^2 = 30

    b^2 - 40b + 30 = 0

    if we apply the general quadratic equation to solve we have:

    b = (40 + - √ (1600 - 120)) / 2

    b = (40 + - √ (1480)) / 2

    b = (40 + - 38.47) / 2

    There are two solutions:

    b1 = (40 + 38.47) / 2

    b1 = 39.24

    b2 = (40 - 38.47) / 2

    b2 = 0.765

    lets use the second solution b2 = 0.765, and substitute in the first equation to find a:

    a*b = 30

    a*0.765 = 30

    a = 30/0.765

    a = 39.216

    so the numbers are 39.216 and 0.765
  2. 22 June, 16:41
    0
    (15x2) = 30, (30 + 10) = 40 ... (P. E. M. D. A. S)
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