Choosing pairs
Choosing pairs
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Total answers
Count how many different pairs you can make from the given items.
How many different pairs can you choose from 4 items? (The order inside a pair does not matter.)
A
B
C
D
What does the generator do?
The generator alternates between sets of 3, 4 and 5 items (labelled A, B, C, …). It asks how many different unordered pairs you can make.
How to solve
List all pairs systematically: first all pairs that contain A, then all the new ones that contain B, and so on. Check with the formula n · (n − 1) / 2 — we divide by two because "A, B" is the same pair as "B, A".
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