Subtraction Pyramids: Each brick is the difference of the two bricks under it, so nothing ever goes negative. This is one of the many kinds of math pyramid we make, and here is how it works, with a video, a worked sample and a pyramid you can try right on this page.
The rule
Each brick is the take-away of the two bricks below it: the bigger number minus the smaller one.
A worked sample
Take away along the base
Look at each pair under a brick and take the smaller from the bigger. 9 and 4: 9 − 4 = 5. 4 and 7: 7 − 4 = 3. 7 and 2: 7 − 2 = 5.
Take away again
Now 5 and 3: 5 − 3 = 2. And 3 and 5: 5 − 3 = 2.
The top
Two 2s: 2 − 2 = 0. The top brick is 0, and a 0 at the top is a perfectly good answer.
Your turn
Try it: take away your way up
Type the bigger-minus-smaller of each pair into the empty bricks, then press Check.
Why it is worth doing
Take-away practice stays gentle here: no brick is ever bigger than the biggest number in the base, so a child is never surprised by a huge number.
Books mentioned
Pyramid Subtraction Adventures
A whole book of take-away pyramids for ages 6 to 9, with numbers kept small at first. Full answers are in the back.
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