Math

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Casey paid $45 for one new tire and one used tyre for his bicycle. The new tire costs $17 more than the used tire. How much did the new tire cost?

I have worked out the answer in my head, ($31) but is there a particular formula I can use or follow.

  • Math -

    Let's new = x, old = y

    x+y = 45

    x= y+17

    y+17+y = 45

    2y+17 = 45

    2y+17-17=45- 17

    2y = 28

    2y/2 = 28/2
    y = 14

    x = y+17

    x = 14+17

    x = 31

    So new tire cost $ 31 and used tire cost $ 14

  • Math -

    Short-cut for sum/difference problems:

    Whenever the sum and difference of two numbers are both given, the bigger number is (sum+difference)/2, and the smaller number is (sum-difference)/2.

    (45+17)/2=31
    (45-17)/2=14

    Most of the time these problems can be solved without pen and paper.

  • Math -

    x + (x + 17) = 45

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