If the average (arithmetic mean) monthly sales of a department store

Question

If the average (arithmetic mean) monthly sales of a department store was y dollars during a certain period of several years, what is the average biannual sales over the same period?

(1) The period includes exactly 4 years.
(2) y = 500.

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chetan2u · Answer

So average monthly sales is y, and biannual or 6-monthly average will be 6y..
it will not depend on number of years,,
For example let y be over x years, so Total sales over x years = 12*x*y=12xy
Now bi annual means 6-monthly or 2 times in a year......So, number of bi-annual in x years = 2x
So average biannual sales =  \frac{12xy}{2x}=6y 
 So x doesn't matter, we just require y..

(1) The period includes exactly 4 years.
so x=4, but we don't require x.

(2) y = 500.
So, answer is 6y=6*500=3000

B

desertEagle · Answer

KarishmaB  please explain this question. What biannual means? how is 2 years average same as average over a certain periods? Kindly explain

KarishmaB · Answer

Biannual usually means 'once in 6 months.' Note that 'biennial' means once in two years but sometimes, we use biannual for that too.

Average biannual sales means average 6 month sales.

Say for a period of n years, average monthly sales of a store is y.

y = Total sales of n years / Total number of months (= n*12)

Over the same period, what will the biannual sales be?

Avg Biannual sales = Total sales of n years / Total number of biannual periods (= n*2)

Note that avg biannual sales is just y multiplied by 6 i.e. the average monthly sales multiplied by 6 to make it 6 monthly sale. 
Hence, we just need the value of y to get the avg biannual sales. We don't need the value of n. Or we need the total sales over the total n years.

Statement 2 tells us that y = 500. So avg biannual sales is 500*6 = $3000
Sufficient alone

Statement 1 tells us that n = 4. It doesn't help us because we don't know the sales of these 4 years. 
Not sufficient

Answer (B)

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If the average (arithmetic mean) monthly sales of a department store

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If the average (arithmetic mean) monthly sales of a department store

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