# 2 finding probability problems

• October 7th 2012, 03:17 PM
m58
2 finding probability problems
Hello,

I've been re-working two problems since yesterday, and have been getting the same (wrong) result every time. Here are the problems:

The probability that a person in the US has type B+ blood is 9%. Five unrelated people in the US are selected at random.
a) Find the probability that all 5 have type B+ blood.

Here, I would convert 9% to .09. Then, $.09 * .09 * .09 * .09 * .09 = .000006$

HOWEVER: the answer key says it is .0000059

b) Find the probability that none of the five types have type B+ blood.

$1 - .000006 = .999994$

then

$.999994 * .999994 * .999994 * .999994 * .999994 = .99997$

HOWEVER:
the answer key says it is .624

c) Find the probability that at least one of the five has type B+ blood.

$1 - .99997 = .00003$

HOWEVER: the answer key says it is .376

The second problem confused me from the get-go. Would you mind giving me a hint on how to start it?
A distribution center receives shipments of a product from 3 different factories in the following quantities: 50, 35, and 25. Three times a product is selected at random, each time without replacement. Find the probability that:
a) All three products came from the third factory?
b) None of the three products came from the third factory?
• October 7th 2012, 03:35 PM
Plato
Re: 2 finding probability problems
Quote:

Originally Posted by m58
Hello,

I've been re-working two problems since yesterday, and have been getting the same (wrong) result every time. Here are the problems:

The probability that a person in the US has type B+ blood is 9%. Five unrelated people in the US are selected at random.
a) Find the probability that all 5 have type B+ blood.

Here, I would convert 9% to .09. Then, $.09 * .09 * .09 * .09 * .09 = .000006$
HOWEVER: the answer key says it is .0000059

b) Find the probability that none of the five types have type B+ blood.

$1 - .000006 = .999994$
then
$.999994 * .999994 * .999994 * .999994 * .999994 = .99997$

HOWEVER:
the answer key says it is .624
c) Find the probability that at least one of the five has type B+ blood.
$1 - .99997 = .00003$
HOWEVER: the answer key says it is .376

$(.09)^5=0.0000059049$

$(.91)^5=0.6240321451$

$1-(.91)^5=0.3759678549$