Which one of the following is not a prime no.

a.71
b.91
c.61
d.31

• 91 is not prime
  
• 9 years agoHelpfull: Yes(4) No(0)
• ans b
  91=13*7
• 9 years agoHelpfull: Yes(3) No(0)
• 91 can be divided by 7,13,1,91
• 8 years agoHelpfull: Yes(2) No(0)
• 7+1 = 8 /2 = 4 so prime
  9+1 = 10/2 = 5 so prime
  3+1 = 4/2 = 2 so prime
  6+1 =7 is not a prime
  so ans. is C (61)
• 9 years agoHelpfull: Yes(0) No(3)
• all the number are not devided by any number but 91 is devided by 13 so the 91 is prime number
• 8 years agoHelpfull: Yes(0) No(0)
• B 13*7=91 so it is not prime number
• 6 years agoHelpfull: Yes(0) No(0)