Intelligent Math Puzzle – Challenge 82

Intelligent Math Puzzle – Challenge 82 shows three crosses of five numbers each. Two are complete and the third has a gap in the middle. The rule connecting the four outer numbers to the centre is the same in all three.

Challenge:

Three crosses are shown. In the first, the top, left, centre, right and bottom numbers are 3, 8, 22, 4 and 6. In the second they are 1, 7, 48, 3 and 9. In the third they are 11, 15, ?, 2 and 5. What number should replace the question mark?

The Answer

The correct answer is 78.

In each cross, add the left number to the top number, then multiply by the right number subtracted from the bottom number:

centre = (left + top) × (bottom − right)

First cross: (8 + 3) × (6 − 4) = 11 × 2 = 22. ✓
Second cross: (7 + 1) × (9 − 3) = 8 × 6 = 48. ✓

Applying the same rule to the third cross: (15 + 11) × (5 − 2) = 26 × 3 = 78.

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