Five Flags in 45 Seconds #2 (difficulty level 36)

If we take the 5 most-guessed flags (US, UK, Canada, Australia & France), then a quiz getting you to name those 5 would be the easiest possible, and would rate a 1 on a scale from 1 to 100. A quiz comprising the 5 least-guessed flags (Bolivia, Equatorial Guinea, Solomon Islands, Gambia and Guinea-Bissau) would rate 100, the hardest possible. All other combinations, obviously, rate somewhere in-between.