Final answer:
The difference between the number of away fans at the semi-final and final is 20.
Step-by-step explanation:
The question asks for the difference between the number of away fans at the semi-final and the final. To find the difference, we subtract the number of away fans at the semi-final from the number of away fans at the final:
Number of away fans at the semi-final: 250 x (4/10) = 100
Number of away fans at the final: 400 x (3/10) = 120
Difference = 120 - 100 = 20
Therefore, the difference between the number of away fans at the semi-final and the final is 20.