Brain Teasers and Puzzles

A box for your workings out:

Hint: A little bit of algebra might help.

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:

(1)      A = D x 5

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

(2) A + 21 = (D + 21) x 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 is exactly seven times the age of Glen:

(3)     B = J x 7

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

(4) B + 8 = (J + 8) x 3

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).