Title (assuming the discount level, it may be unreasonable): When a shopping mall promotes sales, it will give you a 10% discount when you buy 200 yuan (including 200 yuan) and a 20% discount when you buy 500 yuan. Now a man spent 400 yuan and asked him how much he saved by discounting.

Answer: If there is no discount, he should spend X yuan, then 0.8x = 400x = 500 500-400 =100 yuan, which is the money saved.