Question -
Answer -
To find r, let usconsider the given expression,
8Cr – 7C3 = 7C2
8Cr = 7C2 + 7C3
We know that nCr + nCr+ 1 = n + 1Cr + 1
8Cr = 7 + 1C2+ 1
8Cr = 8C3
Now, we know thatif nCp = nCq, thenone of the following conditions need to be satisfied:
(i) p = q
(ii) n = p + q
So from thequestion 8Cr = 8C3,we can say that
Let us check forcondition (i)
r = 3
Let us also check forcondition (ii)
8 = 3 + r
r = 5
∴ The values of‘r’ are 3 and 5.