Question 979969: there is a stack of folders. the probability of drawing out a yellow folder from the stack is 7/12. after 18 yellow folders are taken out, the probability of drawing out a yellow folder now is 4/9. how many yellow folders are there initially?
there are 9 girls in a team. if 6 boys joined the team, then the probability of choosing a boy from the team is 4/7. what is the probability of choosing a boy from the team before the six boys join the team?
the probability of drawing a yellow marble from a bag with 42 marbles is 2/3. how many orange marbles should be taken away to have the probability of drawing a yellow marble from the bag to be 14/15?
there are 45 coins in a jar. the probability of drawing a coin randomly that is not a dime is 11/15. how many nickels should be added to have the probability of drawing a dime to be 2/9?
PLEASE EXPLAIN THANK YOU!!!!
Answer by onlinepsa(22)   (Show Source):
You can put this solution on YOUR website! Q> There is a stack of folders. the probability of drawing out a yellow folder from the stack is 7/12. after 18 yellow folders are taken out, the probability of drawing out a yellow folder now is 4/9. how many yellow folders are there initially?
A> Let us consider there are total 12x folders out of which 7x are yellow.
Now, 18 yellow folders are taken out; remaining yellow folders= 7x-18.
Remaining total folders= 12x-18
Now the probability of a yellow folder is given as (7x-18)/(12x-18).
Thus, (7x-18)/(12x-18) = 4/9
=> 63x-162=48x - 72
=>15x=90
=> x= 6.
Initially there are 7x or 42 folders.
Thanks,
PRD
https://onlinepsa.wordpress.com
|
|
|
