A book store bought copies of a new book by a popular author

[Mike@Magoosh]

A book store bought copies of a new book by a popular author, in anticipation of robust sales. The store bought 400 copies from their supplier, each copy at wholesale price W. The store sold the first 150 copies in the first week at 80% more than W, and then over the next month, sold a 100 more at 20% more than W. Finally, to clear shelf space, the store sold the remaining copies to a bargain retailer at 40% less than W. What was the bookstore's net percent profit or loss on the entire lot of 400 books?
30% loss
10% loss
10% profit
20% profit
60% profit

For a page of percent practice problems, as well as the OA & OE for this particular question, see:
https://magoosh.com/gmat/2013/gmat-quant ... -percents/

Mike

[vipulgoyal]

let the whole sale pric eof one book is 10

150x18 + 100x12 + 150x6 - 4000 ---> 4800 - 4000 --> 800 pofit

profit% 20

[Milovan]

We can look at profit or loss as a weighted average.

1st: 150 books sold per 1,8W price
2nd: 100 books sold per 1,2W price
3rd: 150 books sold per 0,6W price

(3*1,8W + 2*1,2W + 3*0,6W) / 8 = 9,6W / 8 = 1,2W

To find total profit we subtract W and get 0,2W which yields 20% profit. The correct answer is D