The task is to generate the correct answer for a given math problem.

[Q]: Problem: if the cost price of 50 articles is equal to the selling price of 40 articles , then the gain or loss percent is ?
[A]: 25 %


[Q]: Problem: a particular library has 75 books in a special collection , all of which were in the library at the beginning of the month . these book are occasionally loaned out through an inter - library program . if , by the end of the month , 80 percent of books that were loaned out are returned and there are 66 books in the special collection at that time , how many books of the special collection were loaned out during that month ?
[A]: 45


[Q]: Problem: what is the rate percent when the simple interest on rs . 800 amount to rs . 128 in 4 years ?
[A]:
4 %