7+8= 15

15-9=6

6*20= 120 (yuan)

120*4=480 (yuan)

480+20=500 (yuan)

Answer the original 500 yuan money.

Smile 500 yuan 4: 5 That naughty 400 yuan.

Naughty 400+20=420 (yuan) laugh 500-20=480 (yuan)

420:480 =7:8, okay?