Logic & numbers
Two fair, independent coins. What is the chance they match?
One half.
The answer
One half.
The idea
Count equally likely outcomes before grouping them into the result you want.
An example
HH and TT match; HT and TH do not. With three fair independent coins, only HHH and TTT have all three matching: two out of eight outcomes, or one quarter.
Try it
List all eight three-coin outcomes and check the count yourself.
More context
The equally likely outcomes are HH, HT, TH, and TT. Two of four match. Independence and fairness are part of the setup.
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