Question

If 20Pr=6840.find r.

Answer 1

Answer:

3

Explanation:

20Pr = 6840

20*19*18....r times = 6840

20*19*18....r times = 20*19*18

=>r=3

I was lucky because I had to go only 3 places back to obtain 6840.

Can be properly solved by using the general nPr formula i.e. nPr = ((n!)/(n-r)!)