City-Data Forum Solve this math problem? (high school, grades, logic, exams)
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12-13-2007, 01:01 PM
 Location: N of citrus, S of decent corn 32,069 posts, read 40,262,379 times Reputation: 52103

Last night my 6th grade grandson had the following problem: If a cat has five kittens, what is the probability that they will all be female?

Nobody knew how to arrive at the answer, including the other grandmother who taught high school math, and his mother who teaches 4th grade. His answer was 2 1/2, but who knows if it's right?

12-13-2007, 01:10 PM
 Location: San Fernando Valley, CA 1,719 posts, read 5,930,570 times Reputation: 776
hmm, half of 5 is 2.5...and there are only two options:male/female.
I bet it isnt scientific on the probability so I'm guessing its a 50/50 question.
So 2.5 would be correct.

12-13-2007, 01:11 PM
 1,363 posts, read 5,253,878 times Reputation: 845
This is why I was an English major

12-13-2007, 01:18 PM
 25,222 posts, read 36,602,015 times Reputation: 32845
If the answer is a probability then it should be given as a percentage which means he told you 2 1/2 percent.

For each cat born there is a 50/50 chance it will be female (like the previous poster I have doubts about that) so a simple explanation is 5 times .5 which does give you 2.5%.

I know I got the same answer as Hungry For Cheese (Love that name!), but the logic is presented a bit differently.

12-13-2007, 02:08 PM
 Location: Western NY 43 posts, read 142,458 times Reputation: 35
OR -

It could be 16.66% - Because there are 6 ways the delivery could happen

5 females
4 females - 1 male
3 females - 2 males
2 females - 3 males
1 female - 4 males
5 males

In which case your probability is 1/6 ...

hmm..

12-13-2007, 02:18 PM
 1,639 posts, read 4,051,598 times Reputation: 999
3.125% chance

1/2*1/2*1/2*1/2*1/2 since each event is mutually exclusive

12-13-2007, 02:24 PM
 Location: Salt Lake City, UT 520 posts, read 1,668,870 times Reputation: 476
Quote:
 Originally Posted by truckingbronco 3.125% chance
I believe this is the correct answer. Thinking back to my engineering statistics I believe you multiply all the probabilities together. For each kitten there is a 50% chance that it is female. If there are five kittens, the probability that they are all female is (.5)(.5)(.5)(.5)(.5) = .03125.

I could be completely wrong though. I recall getting a 23% on one of the exams in that statistics class. The class average was something like 21%.

Update: This link at wikipedia explains it

http://en.wikipedia.org/wiki/Probability

12-13-2007, 02:44 PM
 Location: San Fernando Valley, CA 1,719 posts, read 5,930,570 times Reputation: 776
Whoa, i missed the part that said ALL female...it isnt 50%
It is the 3.125%...final answer. lol

12-13-2007, 09:29 PM
 Location: Mississippi 6,715 posts, read 11,805,400 times Reputation: 4272
I really like this post. I think we should have a sub-forum that people can post these kinds of questions on. It can be all-encompassing of every subject to include science, english, math, etc.... I think it'd be fun, and it'll also make us realize how much we've forgotten since school.

12-14-2007, 10:17 AM
 Location: Minnesota 206 posts, read 501,886 times Reputation: 82
.03125 or 3.125% as others have said.

I knew the rule for this one off the top of my head, though I tended to get some of my worst grades in math.
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