Three of the following number-pairs are alike in some manner and hence form a group. Which number-pair does not belong to that group?
(NOTE: Operations should be performed on the whole numbers, without breaking down the numbers into its constituent digits. E.g. 13 – Operations on 13 such as adding/subtracting/multiplying etc. to 13 can be performed. Breaking down 13 into 1 and 3 and then performing mathematical operations on 1 and 3 is not allowed.)
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. 14 – 121.
Logic: (1st number - 2)2 = 2nd number
Option 1) 14 – 121 → 14 - 3 = 11 → (11)2 = 121
Option 2) 21 – 361 → 21 - 2 = 19 → (19)2 = 361
Option 3) 18 – 256 → 18 - 2 = 16 → (16)2 = 256
Option 4) 11 – 81 → 11 - 2 = 9 → (9)2 = 81
Thus, 14 - 121 number-pair does not belong to that group.