The second sub-item in the seventh volume of the fourth grade math exercise book is Xiaohong 13 yuan 60, and I just bought stamps of 50 and 80, totaling 20 Yang.

The fourth grade has started to learn linear equations in the next semester. There is no problem in using this equation. The process is as follows:

Solution: It is known that a total of 20 stamps were bought, 50-point ones bought X stamps, and 80-point ones bought (20-x) stamps.

Xiaohong has a 60-degree angle of 13 yuan, which is unary = 10, and a 13 yuan 136.

The equation is 5x+8(20-x)= 136.

5x+ 160-8x= 136

-3x= 136- 160

-3x=-24

x=8

Fifty cents bought eight stamps, and eight cents bought 20-8= 12 stamps.

Xiaohong bought eight 50-cent stamps and 12 80-cent stamps.