Question

The quarterback on a football team completes 70% of his passes. He attempts three passes (assumed to be independent) in a given quarter.
a. What is the probability that he will not complete any passes?
b. What is the probability that he will complete exactly 2 passes?

Answer 1

Let p = probability of completion
Let q = probability of non completion
$$
\large
q=1-p
$$
a.
No completions in three attempts is
$$
\large
q^3
$$
b.
He can complete 2 passes in three ways:
$$
ppq+qpp+pqp
$$
Right?

Answer 2

Ok with you so far.

Answer 3

Will it be a percentage when I get the answer?

Answer 4

No. Question asks for probability. Percentage is the answer when they ask for the chance of something.
Substitute p=0.7 and q=0.3 to get your answers.

Answer 5

a) 0.027
b) 0.441