$ \frac{73}{67}: \frac{57}{55}::\frac{93}{87}: $ ?

Options are :

(1) $\frac{47}{67}$

(2) $\frac{53}{57}$

(3) $\frac{63}{61}$

(4) $\frac{73}{71}$

Source: NTSE 2016-17 Examination Bengaluru

  • $\begingroup$ From NTSE Stage 1 examinations conducted at Bengaluru, India 2016-2017. I know the correct answer and can give it if required, but I don't know the reasoning behind it. $\endgroup$ – Prithvish Baidya Oct 26 '17 at 13:44
  • $\begingroup$ OK, excellent. Could you please edit into the question the information about where it comes from? Sorry to be picky about this, but we try to be scrupulous about attribution here... $\endgroup$ – Gareth McCaughan Oct 26 '17 at 13:52
  • 1
    $\begingroup$ (and Welcome to Puzzling!) $\endgroup$ – Sid Oct 26 '17 at 14:20
  • $\begingroup$ Has a correct answer been given? If so, please don't forget to $\color{green}{\checkmark \small\text{Accept}}$ it :) $\endgroup$ – Rubio Nov 8 '17 at 2:12


There is a pattern in the given fractions

73-67 is 6 and 93-87 is also 6. 73,67 are both prime and (57,55),(93,87) are composite. the next fraction should have both prime numbers with the difference between the numbers as 2 (57-55).


Going by the title of this puzzle and mathematically, answer could be

(4) 73/71


All the given fractions are >1 and so the answer should be and fractions are made up entirely of prime numbers / composite numbers but not a mix. Hence option (4).


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.