Math Is Fun Forum

Hi, just a simple question here : Let's say I have two composite numbers factorized in to prime numbers.

12= 2.2.3

20= 2.2.5

And the question is : If I want a number to be divisible by both 12 and 20, I will re arrange the prime numbers.

So,

60=2.2.3.5

Which I think works perfectly, but it bothers me to know that we aren't using the two other 2's.

So,

240=2.2.2.2.3.5

Why isn't that done ? Am I too complicating things for nothing ? (It's just I would want to understand why ^^)

Thanks for your answer

Hi, please, tell me if my was of solving this problem is good or not : Users of public transport are waiting for the bus: 3 women and 1 man. One of them wears glasses, another gloves, and another a hat. What is the probability that the man has none of these accessories?

Here how :

1:Woman
2:Woman
3:Woman
4:Man
                                               Glasses, Gloves, Hat, Nothing

All possible combinations :

{1,2,3,4} {1,2,4,3} {1,3,2,4} {1,3,4,2} {1,4,2,3} {1,4,3,2} {2,1,3,4} {2,1,4,3} {2,3,1,4} {2,3,4,1} {2,4,1,3} {2,4,3,1} {3,1,2,4} {3,1,4,2} {3,2,1,4} {3,2,4,1} {3,4,1,2} {3,4,2,1} {4,1,2,3} {4,1,3,2} {4,2,1,3} {4,2,3,1} {4,3,1,2} {4,3,2,1}

Probability of the man having nothing : 6/24 or 0,25

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Now here's what the ''real'' answer is : 54/72 or 0,75

I figured that they could have obtained this answer by multiplying 18/24 X3 = 54/72 (In my opinion, this is an error because the question is what is the probability that the man has NONE of these accesories and 18/24 is the probability that he wears one of these objects! Am I correct?) So the ''real'' answer would be 18/72

And last thing that bugs me, if I'm correct in all my previous statements, why is the answer on 72 ? There is 24 possibilities ! Why multiply by 3 ? Does the order of the object change anything ? (WHich isn't logical, if you ask me)

Thank you

Hi, just a question that I've been wondering : Can the brain understand every mathematical idea or you must take some things for granted and trust in them ? Because sometimes I try to understand everything and I find it not that easy ? For example, I can understand simple things like 2+2 =4 but I don't think every concept in math is that clear as adding, substracting, etc.

So my final question in general is, should I try to understand everything about the mecanism of something ( in math) ? What do you people do in these situations ? Do you understand everything like it was your own creation? Thanks

This may seem like a wierd question, but here I go : If I have  8/3 . 8/5 = 64/15 why can't I reduce my two 8's at the beginning ? I can reduce my fractions diagonaly or I can reduce the number above the fraction sign and the other one below it. But why can't I do it in a straight line ? Would it be to hard to explain and I have to take it like it is ? Thank you (I like to understand how things works ^^)

I have just a little question about this : If I toss a coin 5 times, what is the probability of getting 4 tails and 1 head ? I think the answer is 5/32 ? Is this any good ? THanks

Hey everyone...I have a little question : How do you factorise big numbers ?

I could just use my calculator but that would be too long... Is there any technique known that I could use ? Take this number : 2016. I must put it in a tree of factors... But there's too many possibilites ..

Thanks !