Optical De-llusion

Please read the sentence and count the F's:
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FINISHED FILES ARE THE RE-
SULT OF YEARS OF SCIENTIF-
IC STUDY COMBINED WITH
THE EXPERIENCE OF YEARS
How many did you see? For the answer see bottom of page
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The answer is not 3 but six.....most people only count the F's in the long words and forget about the ones in the word 'of' which are pronounced phonetically to themselves as 'ov' or at least that's what I did!! Feel free to post how you got on.