Cost, Price, Discount and Profit

Here is a question from an anonymous visitor.

At Mrs Yu's shop, there were two vases for sale at $630 each. She sold one of them at this price and earned 40% of what she paid for it. She sold the other vase later at 20% discount. If the two vases had the same cost price, how much did Mrs Yu earn altogether?

Solution:

Vase 1: 140% --> $630, so 100% --> $450 (cost price), profit --> $630-$450= $180

Vase 2: 100% --> $630, so selling price is 80% --> $504,  profit --> $504 - $450= $54

Thus, total profit is $180+$54= $234

Note:

The common mistake in this question is the misunderstanding of " earned 40% of what she paid for it ". Students often use $630 x 40% to get the earning of first vase. However, this sentence actually means "what she paid for it " (cost price) is 100%. Therefore, the selling price $630 is 140%.