Answer:2
Step-by-step explanation:
Given
Physics problem requires 20 min
Math problem require 10 min
suppose x question of Physics and y questions of Math are done
so according to the question

Time require for x Physics problem 
Time require for y Math problem 
so,

On solving (1) and (2)
we get
and 
Maximum no of Physics question which can be solved is 2
4*5,2*12,in any even number way