Posted by **Carly** on Friday, September 14, 2012 at 1:38am.

You decide to build a pyramid out of wooden blocks. Each block must rest on the corners off 4 other blocks. If there is one block on top and 36 on the bottom, what is the total number of blocks you will need to complete the pyramid?

- Math -
**Reiny**, Friday, September 14, 2012 at 8:18am
The top layer has 1 block

the 2nd layer from the top has 4 blocks

the 3rd layer from the top has 9 blocks

the 4th has 16 blocks

the 5th has 25 blocks, and

the 6th has s36 blocks

So we have 1+4+9+16+25+36

= 91

btw, there is a formula for the sum of squares of the first n numbers

sumofsquares(n) = n(n+1)2n+1)/6

sumofsquares(6) = 6(7)(13)/6 = 91

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