Numbers from 1 to 60 are written in a row on the cards. They left numbers that are multiples of four, but removed those that are multiples of twelve. How many cards are left?
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- Count cards with every fourth number.
- From these, remove cards with numbers 12, 24, 36, 48 and 60.
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Answer: 10
There are 15 numbers that are multiples of four. Five of them are multiples of twelve, so after removal there are 15 − 5 = 10 cards left.