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Puzzle Details

Alex's child Drew, is exactly one fifth of Alex's age.

In 21 years time, Alex will be exactly twice Drew's age.

Blake's is exactly seven times the age of their child, Glen.

In 8 years time, Blake will be three times the age of Glen.

How old are Drew and Glen now?

Puzzle Copyright © Kevin Stone

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Answer: Drew is 7 years old and Glen is 4 years old.

The first half of the question involves Drew (D) and Alex (A).

Drew is currently one fifth of Alex's age, so:

        A = D x 5           (1)

In 21 years time, Alex will be twice their age, so:

   A + 21 = (D + 21) x 2    (2)

Using (1) in (2) gives:

   A + 21 = (D + 21) x 2

  5D + 21 = (D + 21) x 2

  5D + 21 = 2D + 42

       3D = 21

        D = 7

So Drew is 7 (and Alex is 35).

The second half of the question involves Glen (J) and Blake (B).

Blake's is exactly seven times the age of Glen:

        B = J x 7           (3)

In 8 years time, Blake will be three times the age of Glen, so:

    B + 8 = (J + 8) x 3     (4)

Using (3) in (4) gives:

    B + 8 = (J + 8) x 3

   7J + 8 = (J + 8) x 3

   7J + 8 = 3J + 24

       4J = 16

        J = 4

So Glen is 4 (and Blake is 28).

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