Here we shall use the binomial distribution formula to evaluate the probability:
let the probability that the temp will be above 80 be P(F)=2/3;
Probability that the temp will be below 80 be P(F')=1/3
thus,
The probability that the temp will be above 80 for 20 days for the month of June will be:
P(F)=n!/((n-x)!x!)p^xq^(n-x)
p=2/3 and q=1/3, n=30, x=20
plugging the values in the equation we obtain:
P(F)=30!/(10!*20!)*(2/3)^20*(1/3)^(30-20)
P(F)=0.153