A and B go shopping. It is known that they buy the same quantity of commodities, and the unit price of each commodity is only 8 yuan and 9 yuan. If two people spend 172 yuan to buy goods, how many goods are there in 9 yuan? Solution: The unit price is X in 8 yuan and Y in 9 yuan. When two people buy the same quantity of goods, (x+y) is even. 8x+9y = 172 = & gt； 2(x+y)+y/4=43 Because 2(x+y) is a even number, y/4 must be singular, and y is a multiple of 4. Y = 4, 12, 20 ..., on 20*9= 180 >; 172, y=20, y=4, x= 17, x+y=2 1 is singular, y=4. Y= 12, x=8, which meets the requirements. There are 12 pieces of goods with unit price in 9 yuan.