Answer: There are 10 students who are in both the hockey and football teams.
Step-by-step explanation: We can use the principle of inclusion-exclusion to find the number of students who are in both the hockey and football teams.
The total number of students in both teams is the sum of the number of students in the hockey team and the number of students in the football team, minus the number of students who are in both teams (to avoid double-counting):
Total = Hockey + Football - Both
Substituting the given values, we get:
100 = 40 + 70 - Both
Simplifying, we get:
Both = 40 + 70 - 100
Both = 10
Therefore, there are 10 students who are in both the hockey and football teams.