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September 17, 2014

September 17, 2014

Posted by **Teacher** on Monday, August 4, 2008 at 3:53pm.

If it takes 6 cubes to build 3 steps, how many cubes will be needed for 11 steps?

It sounds so easy but my answer doesn't match the answer sheet. Thanks!

- Math -
**drwls**, Monday, August 4, 2008 at 4:54pmFor N steps, the number needed is

1 + 2 + ... + N

This sum can always be written

N (N+1)/2

N = 11, the number of blocks needed is

11x12/2 = 66

- Math -
**Teacher**, Tuesday, August 5, 2008 at 10:03pmThank you so much!

- Math -

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