2 : 9 :: ?
2 : 9 :: ?
The relationship is: cube of the first number, plus 1, gives the second number. 2 cubed is 8, plus 1 is 9. Checking the options, 3 cubed is 27, plus 1 is 28, which matches. The other options do not follow this rule.
Re-check your working by substituting the answer back into the original question.