SOLUTION: An urn contains 7 one-dollar bills, 5 five-dollar bills, and 3 ten-dollar bills. A person reaches in and takes a bill out, then reaches in and takes another one out (without replac

Algebra ->  Probability-and-statistics -> SOLUTION: An urn contains 7 one-dollar bills, 5 five-dollar bills, and 3 ten-dollar bills. A person reaches in and takes a bill out, then reaches in and takes another one out (without replac      Log On


   

Question 629178: An urn contains 7 one-dollar bills, 5 five-dollar bills, and 3 ten-dollar bills. A person reaches in and takes a bill out, then reaches in and takes another one out (without replacing the first one).
a) what is the probability that a five-dollar bill is taken out first, followed by a one dollar bill?
b) what is the probability that a total of $15 is taken out?
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!
 

Hi,

An urn contains 7 one-dollar bills, 5 five-dollar bills, and 3 ten-dollar bills. 15 bills in ALL

 two bill drawn without replacement

P($5 then $1) = +%285%2F15%29%287%2F14%29+=+1%2F6

P(sum is $15) = P($5 then $10) + P($10 then $5) = %285%2F15%29%283%2F14%29+%2B+%283%2F15%29%285%2F14%29

Re: TY, the format on this site doesn't allow for tree diagrams.

However there are 15C2  or 105 ways of chosing 2 cards: (15 ways for each $1)