How many two digit numbers are there such that the product of their digits after reducing it to the smallest form is a prime number? for example if we take 98 then 9*8=72, 72=7*2=14, 14=1*4=4. Consider only 4 prime no.s (2,3,5,7)

• answer is 18
  
  bcs
  we know prime no. are 2 ,3 , 5, 7
  mulply by 1 is prime no
  
  2 = 21(2*1)=73(7*3)
  2 = 21 (2*1)=37(3*7)
  2= 12(1*2)=43(4*3)or34(3*4)
  or26(2*6)or62(6*2)
  .
  .
  .similarly for all prime no then u will got it....
  
  
  12,13,15,17,21,26,31,34,35,37,43,51,53,57,62,71,73,75
  
  ans is 18
• 9 years agoHelpfull: Yes(49) No(3)
• (this one is 100% right)Explanation:
  2 = 12 or 21 So 1×2, 2×1, 3×4, 4×3, 2×6, 6×2, 3×7, 7×3
  3 = 13 or 31 So 1×3, 3×1
  5 = 15, 51 So 1×5, 5×1, 3×5, 5×3, 7×5, 5×7
  7 = 17 or 71 So 1×7, 7×1
  15 = 3×5 = 5×3
  So total 18 numbers = 12,13,15,17,21,26,31,34,35,37,43,51,53,57,62,71,73,75
  so Ans is >>18
• 9 years agoHelpfull: Yes(15) No(0)
• answer is 18
  ans the numbers are
  12
  13
  15
  17
  21
  26
  31
  34
  35
  37
  43
  51
  53
  57
  62
  71
  73
  75
• 9 years agoHelpfull: Yes(3) No(1)
• answer is 16
  
  bcs
  we know prime no. are 2 ,3 , 5, 7
  mulply by 1 is prime no
  
  2 = 21(2*1)=73(7*3)
  2 = 21 (2*1)=37(3*7)
  2= 12(1*2)=43(4*3)or34(3*4)
  .
  .
  .similarly for all prime no then u will got it....
  
  
  43 , 34 , 57 , 75 , 53 , 35 ,12,13,15,17,37,73,21,31,51,71
  
  ans is 16 no . only satisfy yhe condition
  
• 9 years agoHelpfull: Yes(1) No(8)
• ans is only 18
• 9 years agoHelpfull: Yes(1) No(0)
• 24 is the right ans
• 9 years agoHelpfull: Yes(1) No(9)
• @shubham i also got 16 but 16 was not in the options. Options were 10,14,18 and 24
• 9 years agoHelpfull: Yes(0) No(0)
• ans is 18.for those who are getting 16 please recheck
• 9 years agoHelpfull: Yes(0) No(0)
• Can someone please tell that why we are not considering 14(1*4=4 = 2^2,18=2^3,19 =3^2)..
• 9 years agoHelpfull: Yes(0) No(2)
• 15+51=66
  66+66=132
  132+321=363
  363+363=726
  726+627=1353
• 9 years agoHelpfull: Yes(0) No(2)