The basic rule of combinatorics
Answers are for parents and teachers.
1
A canteen has 4 kinds of soup, 3 main dishes and 2 drinks. Taking one of each, how many different lunch sets can be made?
24
2
How many two-letter codes can be made from the letters a, b, c, d, e if repetition is allowed?
25
3
In how many ways can a pair of pupils on duty be chosen from 12 pupils?
66
4
The menu has 5 main dishes and 3 desserts. In how many ways can one dish (a main or a dessert) be chosen?
8
5
Every two of 7 pupils took one photo together. How many photos were taken?
21