How many 7's immediately preceded by 6 but not immediately followed by 4 are there in the following series?
7 4 2 7 6 4 3 6 7 5 3 5 7 8 4 3 7 6 7 2 4 0 6 7 4 3
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Two
A 7 is counted only if the digit just before it is 6 and the digit just after it is not 4. So every “6 7” in the series is found first, and then the digit after that 7 is checked:
8th to 10th digits, 6 7 5: the 7 is followed by 5, so it is counted
18th to 20th digits, 6 7 2: the 7 is followed by 2, so it is counted
23rd to 25th digits, 6 7 4: the 7 is followed by 4, so it is not counted
