The probability x win a set is 3 in 5, 0.6.
The probability that x wins m sets from a total of N is given by the formula:
[tex]P(MX|N)=\frac{N!}{M!(N-M)!}\cdot0.6^M0.4^{N-M}[/tex]a) If they play 6 sets, the probability that y wins 3 of then is given by:
[tex]P(3X|6)=\frac{6!}{3!3!}\cdot0.6^3\cdot0.4^3=0.276[/tex]b) The probability that y wins at least 5 of then is given by:
[tex]P(1X|6)+P(0X|6)=6\cdot0.4^5\cdot0.6+0.4^6=0.041[/tex]