Question

What is 5a asking???????

Answer 1

`\bf _nC_r\iff \left( \begin{array}{llll} n\\ r \end{array} \right)\iff \cfrac{n!}{r!(n-r)!}\\\\ -----------------------------\\\\ \left( \begin{array}{llll} 40\\ 4 \end{array} \right)\implies \cfrac{40!}{4!(40-4)!}\implies \begin{array}{llll} \cfrac{4!}{4!\cdot 36!}\\ \qquad \uparrow \\ \qquad b \end{array}`