# Selecting money from a bag.

• Sep 27th 2010, 01:48 AM
soni
Selecting money from a bag.
A bag contains 5 ten dollar bills, 7 twenty dollar bills, and 6 fifty dollar bills. What is the probability of drawing.

a)
either ten or twenty dollar bill?

b) either twenty or fifty dollar bill?
• Sep 27th 2010, 01:50 AM
Prove It
How many possible choices are there?

How many of these are "either ten or twenty dollars"?

How many of these are "either twenty or fifty dollars"?

• Sep 27th 2010, 06:26 AM
mr fantastic
Quote:

Originally Posted by soni
A bag contains 5 ten dollar bills, 7 twenty dollar bills, and 6 fifty dollar bills. What is the probability of drawing.

a)
either ten or twenty dollar bill?

b) either twenty or fifty dollar bill?

Try drawing a tree diagram first.
• Sep 27th 2010, 07:25 PM
Prove It
Quote:

Originally Posted by mr fantastic
Try drawing a tree diagram first.

I don't think a tree diagram is going to help...

It's not asking for $\displaystyle Pr(10 \cap 20)$, it's asking for $\displaystyle Pr(10 \cup 20)$...

Surely you can just do $\displaystyle \frac{n(10) + n(20)}{n(\varepsilon)}$...
• Sep 27th 2010, 07:38 PM
mr fantastic
Quote:

Originally Posted by Prove It
I don't think a tree diagram is going to help...

It's not asking for $\displaystyle Pr(10 \cap 20)$, it's asking for $\displaystyle Pr(10 \cup 20)$...

Surely you can just do $\displaystyle \frac{n(10) + n(20)}{n(\varepsilon)}$...

The tree diagram lets the OP visualise the situation. The required probabilities are then easily read from the tree diagram and added together.