What is the probability that a 7-digit phone number contains at least one 8? (Repetition of numbers and lead zero are allowed).

Let's compute the probability that a 7-digit phone number does not contain 8s, at all.

This means that, for each of the 7 digits, we have 9 choices (the ten digits except 8).

So, there are 7-digit phone numbers that don't contain 8s.

Note that the total number of 7-digit phone numbers is , because we have 10 choices (the ten digits) for each of the seven slots.

So, the probability of finding a phone number with no 8s is

This implies that the probability that a 7-digit phone number contains at least one 8 is the complementary probability

b) the dogs need to shift their focus to human scent.

a.

step-by-step explanation:

step 1 distribute 2 to every term in the parentheses

step 2 add 10 on both sides of the equal sign