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.