Count The F's

FINISHED FILES ARE THE RESULT OF YEARS OF SCIENTIFIC STUDY COMBINED 

WITH THE EXPERIENCE OF YEARS.

Count correctly how many 'F' are there in the sentence above. I challenge you! 

Ans:

FINISHED FILES ARE THE
RESULT OF YEARS OF SCIENTIFIC
STUDY COMBINED WITH THE
EXPERIENCE OF YEARS

So the correct answer is 6

Almost everyone guesses three. Why? It seems that the brain cannot correctly process the word "OF". The letter F usually makes the "f" sound, like in "fox". However, in the word "of", it makes a "v" sound. Somehow, your brain overlooks the word "of" as it scans for the sound of "f".