n!Combinatorics: math practice, grade 9

Practise “Combinatorics” online for free. Five right answers in a row make the tasks harder, two mistakes in a row make them easier. Right answers earn coins for games.

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Example problems

These are only examples: the practice makes new tasks every time.

1. Different books go on a shelf in a row. Books: 6. In how many ways can they be arranged?

   Answer

   720

2. Teams in a league: 11. Each plays each other twice, at home and away. How many matches are there?

   Answer

   110

3. Friends meet, 14 of them. Everyone shakes hands with everyone else. How many handshakes are there?

   Answer

   91

4. Friends meet, 6 of them. Everyone shakes hands with everyone else. How many handshakes are there?

   Answer

   15

5. Pupils who want to go to a maths contest: 5. Three must be chosen. In how many ways can it be done?

   Answer

   10

6. How many three-digit numbers with different digits can be made from the digits 1, 2, 3, 4?

   Answer

   24

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