brain teaser or super easy??

emjie · 2011-02-20 00:27:47

OK so i was never much of a math brain and im returning to maths at uni, I have this problem book and im stuck on question 1! OK so here it is...

the average mass of 7 boys is 72 kgs, the average mass of 5 girls is 63kgs. What is the average mass of 12 children?

like i said im not much of a maths brain, but I can't see how i can solve it. I thought maybe id need the average mass of each boy and girl and then google to find the average boy to girl ratio of the world and then add it up the weights and find the average... but that seems far fetched... am i missing something mathsy??

emjie · 2011-02-20 00:28:40

PS you are my new favorite site, expect tohear from mea lot this semester!!:)

Bob · 2011-02-20 00:59:30

hi emjie,

Some people make the mistake of adding the two averages up and dividing by two. Doesn't work though unless there's equal numbers of boys and girls.

What you do is work out the total mass of them all and divide by 12.

So

will get you the total mass. Then divide by 12.

You might find my post #3 on http://www.mathisfunforum.com/viewtopic.php?id=14775 helps too, with general understanding.

Bob

Last edited by Bob (2011-02-20 01:04:44)

emjie · 2011-02-20 11:31:22

thanks so much, really helped.

Bob · 2011-02-20 20:54:39

hi emjie,

You are very welcome.

Bob

Math Is Fun Forum

#1 2011-02-20 00:27:47

brain teaser or super easy??

#2 2011-02-20 00:28:40

Re: brain teaser or super easy??

#3 2011-02-20 00:59:30

Re: brain teaser or super easy??

#4 2011-02-20 11:31:22

Re: brain teaser or super easy??

#5 2011-02-20 20:54:39

Re: brain teaser or super easy??

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