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 1
The correct answer is Option (1) → 375
Compare the middle digit of each number with the sum of its first and last digits.
Option (1) 375 — \( 3 + 5 = 8 \), but the middle digit is 7: does not match.
Option (2) 561 — \( 5 + 1 = 6 \) = middle digit 6.
Option (3) 187 — \( 1 + 7 = 8 \) = middle digit 8.
Option (4) 583 — \( 5 + 3 = 8 \) = middle digit 8.
In 561, 187 and 583 the middle digit is the sum of the other two (so each is a multiple of 11: \( 11 \times 51 \), \( 11 \times 17 \), \( 11 \times 53 \)); 375 does not follow this, so 375 is the odd one out.