Three of the following four numbers are alike in a certain way and one is different. Choose the number that does not belong to the group.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 666
Add the digits of each number.
Option (1) 557 — digit sum \( 5 + 5 + 7 = 17 \).
Option (2) 719 — digit sum \( 7 + 1 + 9 = 17 \).
Option (3) 666 — digit sum \( 6 + 6 + 6 = 18 \), not 17.
Option (4) 647 — digit sum \( 6 + 4 + 7 = 17 \).
The digits of 557, 719 and 647 add up to 17; those of 666 add up to 18, so 666 is the odd one out.