Question

the larger of two numbers is 7 less than three times the smaller number. if the sum of the numbers is 61, find the numbers

Answer 1

Let X = the large #

    Y = the small #

We have 2 unknowns, therefore we need 2 equations to solve for them:

    X + Y = 61

    X = 3Y - 7

Using the substitution method we get:

    X + Y = 61                original equation

   (3Y - 7) + Y = 61        substituting for X

    4Y - 7 = 61                combine like terms

    4Y - 7 + 7 = 61 + 7    add 7 to both sides

    4Y = 68                     simplify

    4Y/4 = 68/4               divide both sides by 4

    Y = 17                       solve for Y

    X + Y = 61                 original equation

    X + 17 = 61                replace Y with 17

    X + 17 - 17 = 61 - 17  subtract 17 from both sides

    X = 44                        solve for X

Check your answer:

       X + Y = 61          X = 3Y - 7

     44 + 17 = 61        44 = 3(17) - 7

     61 = 61  check!     44 = 51 - 7

                                 44 = 44  check!

Therefore, the larger #(X) = 44 and the smaller #(Y)= 17.