The easiest way to do these types of questions is to look at the difference between x and y on a number line. x is at 0.5 and y is at 0.8, and together the average is 0.75. This means that every product checked by x brings down the average by 0.25 and every product checked by y brings up the average by 0.05. To balance these two out, y needs to check 5 products for every time x checks 1 product. Hence 1/6 of total checked by x and 5/6 of total checked by y.

Algebra works too but the number line strategy gets you the correct answer quickly. If you practice doing that, this is a 1-minute question, from starting to read to clicking "next".

Hope this helps!
-Ron
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This is a allegation problem.

We can use a shortcut.

See the attachment for the shortcut.Its a simple one


So X/Y = 0.05/0.25 = 1/5

Therefore the fraction of products checked by Y = 5/6

You can use alligation to solve this.
Ratio X=0.75-0.5=0.25

Ratio Y=0.8-0.75=0.05
Now the ratio y/x is:
\(\frac{Y}{X}=\frac{0.25}{0.05}\) or \(\frac{5}{1}\)

So for 6 products there were 5 Y and 1 X. 5/6 is the answer
If you wanna know more about this method check my signature : mixture!

Hi, I am not aware of allegation. can you please explain about this or point me to some useful but short source.

Differential approach

---50------------75------80----->

25x=5y

x/y=5/25=1/5, so y/x+y=5/6

B

0.5X + 0.8Y = 0.75 ( X + Y )
=> 0.05 Y = 0.25 X
=> Y / X = 5 / 1

Fraction = 5/6

Answer : B

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