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Re: If a is the smallest prime number greater than 21 and b is t [#permalink]
06 Mar 2018, 20:42

1

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The next prime above 21 is 23, since 22 is even. So a is 23.

The greatest prime less than 16 is 13, so b is 13.

Rather than multiply 13 and 23, notice that if you did, the units digit of the number will be 9, since 3x3 is 9. Since A is the only answer ending in 9, the answer must be A.
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