Homework Help: Math

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

I think the answer is wrong online so I would like to know what the correct answer is before I teach a student!

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 4:54pm
For 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 10:03pm
  Thank you so much!

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