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

• 91 is not a prime number as 91 = 13*7
• 12 years agoHelpfull: Yes(9) No(1)
• non prime number among options 31,61,71,91 is 91
• 9 years agoHelpfull: Yes(2) No(1)
• we check whether a no is prime or not by checking its divisibility with:
  if a no
• 9 years agoHelpfull: Yes(1) No(0)
• Simple, as 13 * 7 = 91, so 91 is the correct number.
• 9 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.
• 9 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.
• 8 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..
• 8 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
• 5 years agoHelpfull: Yes(0) No(0)
• 91
  Since it is a multiple of 13 as 13×7=91
• 5 years agoHelpfull: Yes(0) No(0)