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1 vote
Which of these is a prime number 1,11,21,51 ?

2 Answers

5 votes
11,,21,51 are all  prime numbers
User Fadelakin
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4 votes
A prime number has exactly 2 different factors, 1 and itself.

11 is divisible only by 1 and 11.
11 is prime.

21 and 51 have a least three factors. They are not prime.
1 has only 1 factor. 1 is not prime.
User Fsacer
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7.9k points