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March 26, 2017

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Al is twice as old as Bill, who is twice as old as Carl. In 10 years, Al will be twice as old as Carl. How old is Al now?

A. 40
B. 20
C. 10
D. 5

  • math - ,

    I usually start with the smallest quantity, which here is Carl's age

    let Carl's age be x
    then Bill is 2x
    and Al is 4x

    in 10 years:
    Carl --- x+10
    Bill --- 2x+10
    Al ---- 4x + 10

    so 4x+10 = 2(x+10)
    4x + 10 = 2x + 20
    2x = 10
    x = 5

    So now Al is 4(5) = 20

    check:
    present ages:
    Carl -- 5
    Bill --- 10
    Al ---- 20

    10 years from now:
    Al will be 30 and Carl will be 15
    Is Al twice as old as Carl ?? YES

  • math - ,

    thanks

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