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April 11th, 2018, 12:02 AM   #1
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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.
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April 11th, 2018, 12:05 AM   #2
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Quote:
Originally Posted by Ganesh Ujwal View Post
$\displaystyle \frac {30(X) + 30(Y)}{X+Y}$
What is this supposed to do?? Is this supposed to be the average weight? Where does this (wrong) formula come from?
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April 11th, 2018, 12:11 AM   #3
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Quote:
Originally Posted by Micrm@ss View Post
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?
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April 11th, 2018, 12:14 AM   #4
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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
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April 11th, 2018, 12:15 AM   #5
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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.
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April 11th, 2018, 12:16 AM   #6
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Originally Posted by Ganesh Ujwal View Post
So what is the right formula?
Replace X + Y with 60, since there are 60 students total.
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