## Problem of the Day #399: Rainbow Grid
*April 21, 2012*

*Posted by Saketh in : potd , trackback*

Using his crayons, Sohail draws a $10$ by $10$ grid of unit squares. For each of the $220$ unit segments he draws, he picks one of $7$ different colors.

After finishing, Sohail observes that each cell has two sides of one color, and two sides of another. How many different ways could he have drawn the grid?

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