Medium
In each circle, the number in the centre is related to the four numbers around it.
Circle 1: outer numbers 2, 4, 6, 8 → centre 10
Circle 2: outer numbers 1, 3, 5, 7 → centre 8
Circle 3: outer numbers 3, 5, 7, 9 → centre ?
Explanation
Explanation
Step 1: Add the outer numbers in Circle 1: 2 + 4 + 6 + 8 = 20, and the centre is 10, which is 20 ÷ 2.
Step 2: Test Circle 2: 1 + 3 + 5 + 7 = 16, and 16 ÷ 2 = 8 ✓. So the centre = half of the sum of the outer numbers.
Step 3: Apply to Circle 3: 3 + 5 + 7 + 9 = 24.
Step 4: Centre = 24 ÷ 2 = 12.
Answer: 12.
PRO TIP
Re-check your working by substituting the answer back into the original question.