The two numbers add up to twice the average. The larger is one unit plus 4; the smaller is one unit.

Smaller?Larger?4diff 4total = 2 × 15 = 30

Plain numbers are given; italic underlined numbers are worked out.

  1. Total → 2 × 15 = 30
  2. 2 units + 4 → 30
  3. 2 units → 30 − 4 = 26
  4. 1 unit (smaller) → 26 ÷ 2 = 13
  5. Larger → 13 + 4 = 17

The larger number is 17 and the smaller number is 13.

Check: (17 + 13) ÷ 2 = 15 and 17 − 13 = 4. ✓