How many total bills are there? (picking $10 from bag w/...)

[Christinayo]

I have been having a lot of problems with my homework lately. One of the questions I am stuck on is this:

"The probability of picking a $10 from a bag of $1, $5, and $10 bills is 2/3. The probability of picking a $5 is 3/10. There are two $1 bills in the bag. How many total bills are there?

It would be great if someone got back to me on this I think I have to find a common factor between the numerator and denominator, but I'm not sure

 

[Denis]

Re: How many total bills are there?

If (example) bag contains 3 1's , 4 5's and 7 10's, probability of picking a 5 is 4/14 = 2/7 : do you follow that?

If so, to solve your problem:
let f = number of 5's and t = number of 10's; since we have 2 1's (given) then:
t / (2 + f + t) = 2/3
f / (2 + f + t) = 3/10
You can solve that for f and t

If not, you need classroom help.