How many such 5s are there in the following number series, each of which is immediately preceded by 3 or 4 but not immediately followed by 8 or 9? 3 5 9 5 4 5 5 3 5 8 4 5 6 7 3 5 7 5 5 4 5 2 3 5 1 0

Check every 5 with a 3 or 4 just before it: 3-5-9 (no, followed by 9), 4-5-5 (yes), 3-5-8 (no), 4-5-6 (yes), 3-5-7 (yes), 4-5-2 (yes), 3-5-1 (yes). That gives five such 5s, so 1, 2 and 3 are all wrong.