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 April 11th, 2018, 12:02 AM #1 Senior Member   Joined: Aug 2014 From: India Posts: 294 Thanks: 1 Find the average weight of the total students. The average weight of 30 students is x kg and the average weight of another 30 students is y kg. The ratio of x and y is 2:3. Find the average weight of the total students. I tried: $\displaystyle \frac {30(X) + 30(Y)}{X+Y}$ $\frac {X}{Y}$= $\displaystyle \frac{2}{3}$ X = $\displaystyle \frac {2Y}{3}$ $\displaystyle \frac {30(\frac {2}{3})Y + 30Y}{\frac {2}{3}Y+Y}$ $\displaystyle 3 \frac{20Y+30Y}{2Y+3Y}$ $\displaystyle 3(10) \frac{5y}{5y}$ = 30 But answer is $\displaystyle \frac {X+Y}{2}$ Last edited by Ganesh Ujwal; April 11th, 2018 at 12:10 AM.
April 11th, 2018, 12:05 AM   #2
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Quote:
 Originally Posted by Ganesh Ujwal $\displaystyle \frac {30(X) + 30(Y)}{X+Y}$
What is this supposed to do?? Is this supposed to be the average weight? Where does this (wrong) formula come from?

April 11th, 2018, 12:11 AM   #3
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Quote:
 Originally Posted by Micrm@ss What is this supposed to do?? Is this supposed to be the average weight? Where does this (wrong) formula come from?
So what is the right formula?

 April 11th, 2018, 12:14 AM #4 Senior Member   Joined: Oct 2009 Posts: 428 Thanks: 144 I'm just pretending to be an expert according to some people, so I'm sure you wouldn't want my help! http://mymathforum.com/feedback/3438...questions.html
April 11th, 2018, 12:15 AM   #5
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 Originally Posted by Micrm@ss I'm just pretending to be an expert according to some people, so I'm sure you wouldn't want my help! http://mymathforum.com/feedback/3438...questions.html
That depends on your answer. Now tell me the answer.

April 11th, 2018, 12:16 AM   #6
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Quote:
 Originally Posted by Ganesh Ujwal So what is the right formula?
Replace X + Y with 60, since there are 60 students total.

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