Read the row of digits below from left to right.
2 3 4 6 5 6 7 1 4 5 7 8 9 2 1 2 3 5 4 3 6 7 8 0 3
How many digits in this row have, directly before them, the digit one less than themselves and, directly after them, the digit one more than themselves?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 5
Look at each digit with its two neighbours: for a digit d, the digit before it must be d − 1 and the digit after it must be d + 1, so the three digits must read upwards in steps of one, like 3 4 5. A run read downwards, such as 5 4 3, does not count. Going along the row, the upward runs of three are:
Places 1 to 3: 2 3 4 — the middle digit 3 counts
Places 5 to 7: 5 6 7 — the middle digit 6 counts
Places 11 to 13: 7 8 9 — the middle digit 8 counts
Places 15 to 17: 1 2 3 — the middle digit 2 counts
Places 21 to 23: 6 7 8 — the middle digit 7 counts
No other digit has the digit one less just before it and the digit one more just after it; the first and the last digits have only one neighbour each.
So the answer is 5.