I would go for [A], what is the OA?

Another image, I can't view

mleviko wrote:I would go for [A], what is the OA?

Interesting question - What is the right answer?

In my opinion the answer should be E.

Standard Deviation remains same if the same amount is added/subtracted, from each individual. So we know that same amount is added/subtracted from each individual the standard deviation did not change.

The conversion between average and standard deviation, and vice versa, is impossible, if there individual items are missing...

A tells us that same percentage was removed from each tank, but says nothing about the actual amount and thus insufficient.

Well the OA
is A

i.e we can can get the answer from 1st statement only.

No idea how std deviation concept can be applied here and what to use?

Well, if you substract from each individual the same proportionate amount, the standard devation from the average remains the same. And because we're told the exact std we can answer the question with statement (1).

Well did some simple calculations and it turns out that there is a direct relation between the individual items and standard deviation.

When all the elements are increased/decreased by same percentage, standard deviation also increases/decreases by the same percentage

So in the question, the standard deviation will also decrease by 30% and become 7

mleviko wrote:Well, if you substract from each individual the same proportionate amount, the standard devation from the average remains the same. And because we're told the exact std we can answer the question with statement (1).

Close! If it's a proportionate amount, the SD will change proportionally.

If we subtract the same amount from each individual term, then SD remains the same.