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L is 3 times as old as D, who is five yrs older than C. If in 18 years L will be twice as old as c will be then, how old is D?

  • math -

    L = 3D
    D = C + 5
    L + 18 = 2(C +18)
    First eliminate one of the variables. I will use the first two equations to eliminate D.
    L = 3(C+5) = 3C + 15
    L = 2C + 18
    Those two equations tell you, by setting 2C + 18 = 3C + 15, that
    C = 3; so L = 24
    D = 8.

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