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: D
Explanation
The correct answer is option 4 i.e. 15 – 240.
Logic: second number = first number × (first number - 1)
1. 21 – 420: 21 × 20 = 420
2. 22 – 462: 22 × 21 = 462
3. 18 – 306: 18 × 17 =306
4. 15 – 240: 15 × 14 = 210