Brain Teasers and Puzzles

A box for your workings out:

Hint: The number is less than 100.

Answer: 4.

4's double is 8 and 4's quarter is 1.

If the missing number is N, then:

  2N = N + 7
       -
       4

Multiply throughout by 4:

  8N = N + 28

Subtract N from both sides:

  7N = 28

Divide throughout by 7:

   N = 4