Question

If ⁿC₄ = 70 ,then find n.

Options

• 4

• 8

• 5

• 6

Answer 1

8

Explanation:

ⁿC₄ = 70

On n = 8

L.H.S = ⁸C₄ = `(8!)/((8 - 4)!4!)`

= `(8 xx 7 xx 6 xx 5 xx 4!)/(4! xx 4!)`

= `(8 xx 7 xx 6 xx 5)/(4 xx 3 xx 2 xx 1)` = 70

At n = 8, equation satisfied.