# 2 finding probability problems

• Oct 7th 2012, 02:17 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, \$\displaystyle .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.

\$\displaystyle 1 - .000006 = .999994 \$

then

\$\displaystyle .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.

\$\displaystyle 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?
• Oct 7th 2012, 02:35 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, \$\displaystyle .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.

\$\displaystyle 1 - .000006 = .999994 \$
then
\$\displaystyle .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.
\$\displaystyle 1 - .99997 = .00003 \$
HOWEVER: the answer key says it is .376

\$\displaystyle (.09)^5=0.0000059049\$

\$\displaystyle (.91)^5=0.6240321451\$

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