1. Class A and Class B have a total of 83 people, Class B and Class C have a total of 86 people, Class C and Class D have a total of 88 people. How many people are there in Class A and Class D?
1.【Solution】The total number of people in classes A, B, C, and D: $83+88=171$ (people) Subtracting the number of people in classes B and C from the total number of people will give the number of people in classes A and D: 171
$$
-86=85 \text { (people) }
$$