Please help me with this question..

Dear Student,

Let X be the number of right answers in the 5 questions. 
X can take values 0,1,2...5.
X follows a binomial distribution with n =5
.$$\begin{gathered} p\mathit{ }=\mathrm{probability} \mathrm{of} \mathrm{guessing} \mathrm{right} \mathrm{answer} = \frac{1}{3} \\ q =\mathrm{probability} \mathrm{of} \mathrm{guessing} \mathrm{wrong} \mathrm{answer} = \frac{2}{3} \\ \mathrm{Hence}, \mathrm{the} \mathrm{distribution} \mathrm{is} \mathrm{given} \mathrm{by} \\ P(X=r)={}^{5}C_r{\left( \frac{1}{3} \right)}^r{\left( \frac{2}{3}\right)}^{5-r} , r=0,1,2,...5 \\ \therefore P(\mathrm{The} \mathrm{student} \mathrm{guesses} 4 \mathrm{or} \mathrm{more} \mathrm{correct} \mathrm{answers}) = P(\mathrm{X}\ge 4) \\ = P(X=4)+P(X=5) \\ ={}^{5}C_4{\left(\frac{1}{3}\right)}^4{\left(\frac{2}{3}\right)}^1+{}^{5}C_5{\left(\frac{1}{3}\right)}^5{\left(\frac{2}{3}\right)}^0 \\ = \frac{10+1}{3^5} \\ =\frac{11}{243} (option 3). \end{gathered}$$

Regards!