Hypothetical method:
50×20= 1000 (yuan)
1000-880= 120 (yuan)
20- 15=5 (yuan)
15 yuan movie ticket: 120÷5=24 (Zhang)
20 yuan's movie ticket: 50-24=26 (Zhang)
Equation method, let 15 yuan have x, then 20 yuan has (50-x).
15x+20*(50-x)=880
The solution is x = 24,50-x = 24 (hope to adopt! )