If nPr = 840 and nCr = 35, find the value of r.
Given: nPr = 840 and nCr = 35
To find: r=?
We know that:
nCr =
and
nPr =
⇒ nPr= nCr×r!
⇒840=35×r!
⇒
⇒r!=4!
⇒r=4
Ans:r=4