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! )