Hard
Find the missing term: 11 : 17 :: 53 : (?)
Explanation
Explanation
11 is the 5th prime number and 17 is the 7th prime number - a jump of 2 positions in the list of primes. 53 is the 16th prime number, so counting 2 positions further in the list of primes (...47, 53, 59, 61) gives the 18th prime, which is 61.
PRO TIP
Re-check your working by substituting the answer back into the original question.