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7 February, 15:37

The sum of two numbers is 18. Twice the first number plus three times the second number equals 40. Find the numbers.

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  1. 7 February, 18:10
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    a+b=18

    2a+3b=40

    Here's two solutions:

    A) Multiply the first equation by (-2) & sum then the two equations, resulting ''b''. Or, multiply that first equation by (-3) Summing them you get ''a''. Whatever you obtain, introduce it into an equation and obtain the other one.

    B) You have a system of two equation with two unknown terms. Get one unknown term (e. g. ''a'') out of the first equation (a=18-b) & introduce it (18-b) into the other equation, the second one, instead of that unknown term, and you'll get this second equation written within just one unknown term (2 (18-b) + 3b=40; 36-2b+3b=40. With the term this way defined, you'll have also the first one.

    x+y=18; 2x+3y=40

    y=18-x, 2x+3 (18-x) = 40

    2x+54-3x=40

    -x=-14

    x=14

    14+y=18, y=4

    14+4=18

    2 (14) + 3 (4) = 40, 28+12=40
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