Question

Find no of ways to select 10 balls from a large pile of red white and blue balls if the selection has at most 2 red balls

Answer 1

Answer:

Step-by-step explanation:

My working:

(x+x2+x3+...)3

=x3(1+x+x2+...)3

=x3∑∞r=0(r+3−1r)xr

=∑∞r=0(r+2r)x3+r

Hence the number of ways is (2n−12n−3)=(2n−12).

However, the actual answer is (2n+22)−3(n+12). Did i go wrong somewhere in my proof? Or is it some conceptual understanding gone wrong? Thanks!