Question

${}^7{P}_r$ = 840 and ${}^7{C}_r$ = 35. Find r.

• A. 3
• B. 4
• C. 5
• D. 6

Answer 1

The correct option is B

4

$\frac{7!}{(7-r)!}$ = 840

$\frac{7!}{(7-r)!r!}$ = 35

Divide one by the other, we get r = 4.