How many five-digit prime numbers can be obtained by using all the digits 1, 2, 3, 4 and 5 without repetition of digits?
Zero
One
Nine
Ten
A number is prime if it is divisible by only 1 and itself. Now take the digits 1,2,3,4 and 5 and add them. We get 15 as the sum. “If the sum of the digits of a number is divisible by 3 then number will be divisible by 3”. So any number formed using these five digits will be divisible by 3. So it cannot be prime. Hence zero.
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