# Not making sense...probability

• Oct 13th 2008, 09:05 AM
Evergreen
Not making sense...probability
30% of calls to an airline reservation phone line result in a reservation being made.
a. Suppose that an operator handles 10 calls. What is the probability that none of the 10 calls results in a reservaion?
b. What assumption did you make in order to calculate the probability in part (a)
c. What is the probability that at least one call results in a reservation being made?

This probably won't be my last question. I'm not understanding statistics much and I've never been great shakes at maths. Thanks!
• Oct 13th 2008, 05:15 PM
pickslides
Quote:

Originally Posted by Evergreen
30% of calls to an airline reservation phone line result in a reservation being made.
a. Suppose that an operator handles 10 calls. What is the probability that none of the 10 calls results in a reservaion?
b. What assumption did you make in order to calculate the probability in part (a)
c. What is the probability that at least one call results in a reservation being made?

This probably won't be my last question. I'm not understanding statistics much and I've never been great shakes at maths. Thanks!

Looks Binomial to me.

when X is Bi(n=no of trials,p=probabilty of success)
Use P(X=x) = nCx p^x(1-p)^n-x

with:
p (prob of reservation being made) = .30
n = 10

a. P(X=10) = 10C10(.3)^10(1-.3)^10-10

b. each call was independant of the next.

c. P(X>=1) = P(X=1)+P(X=2)+P(X=3)+....+P(X=10)
= 1-P(X=0)
= 10C0(.3)^0(1-.3)^10-0
• Oct 13th 2008, 05:30 PM
mr fantastic
Quote:

Originally Posted by pickslides
Looks Binomial to me.

when X is Bi(n=no of trials,p=probabilty of success)
Use P(X=x) = nCx p^x(1-p)^n-x

with:
p (prob of reservation being made) = .30
n = 10

a. P(X=10) = 10C10(.3)^10(1-.3)^10-10

b. each call was independant of the next.

c. P(X>=1) = P(X=1)+P(X=2)+P(X=3)+....+P(X=10)
= 1-P(X=0)
= 10C0(.3)^0(1-.3)^10-0

I agree. Except that part (a) requires Pr(X = 0), not Pr(X = 10).
• Oct 13th 2008, 05:54 PM
pickslides
Quote:

Originally Posted by mr fantastic
I agree. Except that part (a) requires Pr(X = 0), not Pr(X = 10).

Yep, I did not see the "none" part in part a)

P(X=0) it is.