In a wrong-brick puzzle the pyramid is complete, and every number is filled in, but one brick is wrong. Your job is to find it. There is a method that works every time. We call it counting the complaints.
The idea
Every brick must be the sum of the two below it. If it is not, that pair has a complaint. A wrong brick makes the pairs around it complain. So the wrong brick is where the complaints meet.
A worked example
The rule is the same for every wall: every brick is the sum of the two below it. Here is a wall where one brick is wrong. The shaded bricks are the ones we check at each step.
Four rows, one liar
Bottom: 6, 2, 9, 4. Next: 8, 12, 13. Then 19 and 24. Top: 43. Let's check every pair.
Check the bottom pairs
6 + 2 = 8, which matches. 2 + 9 = 11, but the wall says 12. A complaint! 9 + 4 = 13, which matches.
Check the next pairs
8 + 12 = 20, but the wall says 19. A complaint. 12 + 13 = 25, but the wall says 24. A complaint.
Check the top
19 + 24 = 43. The top agrees with the two bricks under it, so no complaint here.
Find the meeting point
Three complaints, and all of them point at the brick that says 12. It is one of the pair that disagrees below, and one of the pair that disagrees above. The wrong brick is 12, and it should be 11. Check: 8 + 11 = 19 and 11 + 13 = 24.
What the complaints tell you
- A brick in the middle: up to three complaints, one below and two above.
- A brick on the bottom row: nothing below it, so only up to two complaints above.
- The top brick: only one complaint, from the pair under it.
- Two complaints side by side: they share a brick underneath, and that brick is the suspect.
Two things to watch for
Always check all the pairs, because a brick that matches the pair below it can still be the culprit if the pair above does not match. And when you find the suspect, work out what it should be and check it fits both ways, below and above.
Books mentioned
Find the Wrong Brick
130 mistake-hunt puzzles for teens and adults: one brick in each pyramid is wrong, and you find it. The whole book is this one kind of puzzle.
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Escape the Pyramid, Level 2
The same adventure with harder chambers and 8 puzzle kinds, of which number pyramids are only one.
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