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 %
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Q: Problem: the ratio between the sale price and the cost price of an article is 12 : 7 . what is the ratio between the profit and the cost price of that article ?

A: 5 : 7
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Q: Problem: if 7 spiders make 7 webs in 7 days , then how many days are needed for 1 spider to make 1 web ?

A:
7
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