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Probability questions
Posted:
Mon Nov 26, 2012 9:24 pm
by qwerty123
My worst math questions are the probability ones. I always skip them w/ out even looking at them. These and sometimes some hard geometry ques are only ones that I actually skip.
Help me out on this one:
Lisa shakes her piggy bank which contains 5 quarters and 5 nickels until 5 coins fall out with equal probability, what is the probability that the sum of the change that has fallen out is $0.85?
So far, all I know is that 3 Q and 2 N can only add up to $.85 and I'm just lost after that.
Re: Probability questions
Posted:
Wed Nov 28, 2012 11:24 pm
by jagui15
This problem can be solved with combinations. Like you said only 3Q and 2N can work.
You have 5Q but you only want 3Q. So you can make 5nCr3 combinations.
You have 5N but you only want 2N. So you can make 5nCr2 combinations.
When you multiply these you get the number of combinations that results in a sum of .85.
But since you want probably you have to get the total number of combinations. 10 coins total but you only want 5. So there are 10nCr5.
So your answer should be 5nCr3*5nCr2/10nCr5=25/63
Re: Probability questions
Posted:
Fri Nov 30, 2012 7:37 pm
by 101dalmatians
Man - you just defied the law of MAth Marathon! Please. Let us ALL contribute to this amazing feature of this forum... Post ALL your questions over there - at Math Marathon
Here is the link if you don't know...
viewtopic.php?f=4&t=3450Also, follow the instructions on that page!
Re: Probability questions
Posted:
Sun Dec 02, 2012 11:35 pm
by qwerty123
Box A contains 6 red balls and 2 green balls. Box B contains 4 red balls and 3 green balls. A fair die is thrown. If an even number is obtained, a ball is selected from box A; if an odd number is obtained, a ball is selected from box B. If a red ball is selected, what is the probability that it came from box B?
Anyway, I'm just trying to expand my knowledge on prob by doing different types of them.
Re: Probability questions
Posted:
Mon Dec 03, 2012 4:48 am
by Zubair_Marediya
Re: Probability questions
Posted:
Fri Jan 11, 2013 11:37 pm
by qwerty123
Help on Inv. A 2012 #22
Re: Probability questions
Posted:
Fri Jan 11, 2013 11:43 pm
by 007math