# Find the average weight of the total students.

#### Ganesh Ujwal

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:

#### [email protected]

$$\displaystyle \frac {30(X) + 30(Y)}{X+Y}$$
What is this supposed to do?? Is this supposed to be the average weight? Where does this (wrong) formula come from?

#### Ganesh Ujwal

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?

#### Monox D. I-Fly

So what is the right formula?
Replace X + Y with 60, since there are 60 students total.

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