The number of ways of selecting 10 balls from the unlimited number of red, green, white and yellow balls, if selection must include 2 red and 3 yellow balls, is

Number of 10 balls selections= coefficient of x10 in x2+x3+…1+x+x2+…(1+x+x2+…x3+x4+…= coefficient of x5 in (1 + x + x2 +…)4= coefficient of x5 in (1 – x)–4=(4+5−1)C5=8C5=56 ways .