Which one of the following is not a prime number 31 61 71 91

non prime number among options 31,61,71,91 is 91
10 years agoHelpfull: Yes(2) No(1)
we check whether a no is prime or not by checking its divisibility with:
if a no
10 years agoHelpfull: Yes(1) No(0)
Simple, as 13 * 7 = 91, so 91 is the correct number.
10 years agoHelpfull: Yes(1) No(0)
sqrt(91)=approx 9.x so we take 9 prime no. less than 9 are 2,3,5,7 and 91 is divisible by 7 so 91 is not prime number.
10 years agoHelpfull: Yes(1) No(0)
n^2 > number to be find.
where n is the highest square possible value nearest to the number
1. For 31,
6^2 > 31. prime number below 6 are 2,3,5. If 31 is divide my any one of these number, then it is not a prime number.
4. For 91
11^2 >91. Prime numbers below 11 are 2,3,5,7,9.
91 can be divided by 7. so it is not a prime number.
9 years agoHelpfull: Yes(0) No(0)
91
HERE 91 IS NOT A PRIME NUMBER.BECAUSE,13*7=91 SO,91 IS NOT A PRIME NUMBER..
9 years agoHelpfull: Yes(0) No(0)
91, because it is divisible by 7
7 years agoHelpfull: Yes(0) No(0)
91 is a multiple of 7. so, it is not a prime number
6 years agoHelpfull: Yes(0) No(0)
91
Since it is a multiple of 13 as 13×7=91
6 years agoHelpfull: Yes(0) No(0)

Which one of the following is not a prime number?
31
61
71
91