How many 7s 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 3
The correct answer is Option (3) → Two
Look at every 6 that is followed at once by a 7, and then check the number just after that 7; the 7 counts only if that number is not 4.
Terms 8–10: 6, 7, 5 — the 7 is followed by 5: counts
Terms 18–20: 6, 7, 2 — the 7 is followed by 2: counts
Terms 23–25: 6, 7, 4 — the 7 is followed by 4: does not count
The other 7s (terms 1, 4, 13 and 17) are not preceded by 6, so there are two such 7s.