How many numbers are there from 1 to 80 (including 1 and 80 ) such that there reciprocal is non terminating . Eg 1/3 (.3333....is non terminating , similarly 1/11 is non terminating .

• ans will be 66.
  Exp: from 1 to 10 // 3, 6 , 7, 9 =4
  so multiple of 3 also produce non-term. no's when numerator is 1, eg = 6,9,12,15, 18----- 78.
  similarly, multiple of 7 also like= 14, 21, 28------ 77.
  
  And all prime no's greater or eql than 7 also results into non-term. no's like = 7,11,13,17,19, ---- and so on. [ 5 not included b'coz 1/5 = 0.2 i.e, a terminating no.]
  calculate and u will get result 66.
• 9 years agoHelpfull: Yes(7) No(2)
• all the multiples of 3 i.e : 3,6,9......78
  number of terms is 78=3+(n-1)3 => n=26
  all the multiples of 7 i.e : 7,14,21......77
  number of term is 77= 7+(n-1)7 => n=11
  all the multiple of 11 : 11,22,33,44,55,66,77 that is 7
  now exclude the repeated terms 33,66 since it is already divided by 3 and has already been covered.
  As a result you would see 3,7,11 all are prime number that's why you have to calculate for all prime number less then 80. i.e : 13,17,19,23,29,31.. so on
  
• 9 years agoHelpfull: Yes(6) No(0)
• Take all the prime numbers and their multiples that are less than 80.Start from 3.(exclude 2)
  ex. all multiples of 3 that are less than 80 give non terminating reciprocals.Similarly take other prime no.s and their multiples.now remove the repeating numbers ex.21 is a multiple of both 3 and 7.Hence it should be taken only once.
  finally the answer is 66.
  
  or simply take the numbers that give terminating reciprocals.
  i.e 1,2,4,5,8,10,16,20,25,32,40,50,64,80
• 9 years agoHelpfull: Yes(5) No(7)
• ans will be 66
• 9 years agoHelpfull: Yes(4) No(7)
• ans is 66.only 1 2 4 5 8 10 16 20 25 32 40 50 64 80 are terminating.so no. of non-terminating no.are 80-14 =66
  
• 9 years agoHelpfull: Yes(3) No(0)
• please someone give detail and proper answer.
  
• 9 years agoHelpfull: Yes(2) No(0)
• 24 is the answer
• 9 years agoHelpfull: Yes(1) No(0)
• 34
  
  the numbers multiple of 3 or multiple of 7 - the numbers multiple of 21
• 9 years agoHelpfull: Yes(0) No(0)
• ans. is 58
• 9 years agoHelpfull: Yes(0) No(0)
• 30(chech divisible of 3 and 11)
• 9 years agoHelpfull: Yes(0) No(0)
• multiples of 2 and 5 are always terminating like 1/2, 1/4, ......., and 1/5, 1/10, 1/15......., so the total multiples of 2 ( between 1 and 80) are 40 and multiples of 5 are 16 and total are 40+16= 56. But some of them are multiples of 2*5 ie 10 that are included 2 times of multiples of 10 are 8 , thus requred number is 56-8=48, 48 is the answer
• 9 years agoHelpfull: Yes(0) No(3)