Grid + Combination.
Probability
Level
4
Consider a 9 by 6 grid made up of 10 vertical lines and 7 horizontal lines.Find total number of different rectangles in it . Each unit of the grid is a square of same size .
The answer is 945.
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1 solution
For forming a rectangle, you have to choose 2 lines from the 10 vertical lines and 2 lines from the 7 horizontal lines and thus the answer is 10C2 * 7C2