Here's one that's not really a math puzzle, but since we delved into psychological phenomena in the first thread, I figured it was fair game.

Count the number of times the letter F appears in the following sentence:

FINISHED FILES ARE THE RESULT OF YEARS

OF SCIENTIFIC STUDY COMBINED WITH THE

EXPERIENCE OF YEARS.

(just giving you some space here so you don't see the answer before solving the problem)

There are 6, but many people only find 3 at first. If you only found 3, try it again. If you still can't find all 6, keep trying until you do. There isn't a trick in the instructions; there really are 6 "F"s in the capitalized sentence.

If anyone really can't find them, I'll post an explanation pointing them out. I find this puzzle intriguing because I found 3 at first, then when I was told there were 6 I went over the sentence very carefully (I thought) and still didn't find the others. I'm curious to know how many you find initially, and if it wasn't all 6, how difficult it was for you to find the rest of them.

Marion