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Q. The number of (staircase) paths in the $x y$-plane from $(0,0)$ to $(7,5)$ where each such path is made up of individual steps going one unit upward $(U)$ or one unit to the right $(R)$. One such path is shown in figureMathematics Question Image

Permutations and Combinations

Solution:

The number of paths
$=\text { the number of ways of arranging } 5 U^{\prime} S \text { and } 7 R^{\prime} \text { s. } $
$=\frac{12 !}{5 ! 7 !}={ }^{12} C_5$