Question 47461
    40 students enrolled in three areas of study.
LET US USE A ^ B TO SHOW A INTERSECTION B
    23 students in music(S..SAY)
    25 students in math(M..SAY)
    27 students in comp. science(C...SAY)
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 7 took mathematics and music only=M&S ONLY
    5 took music and computer science only=S&C ONLY
    6 took math and comp. sci. only=M&C ONLY 
    7 took all three subjects=M&C&S=7
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HENCE THOSE WHO TOOK MATHS ONLY = M-M&S ONLY-M&C ONLY - M&S&C=25-7-6-7=5  
THOSE WHO TOOK MUSIC ONLY = S-S&M ONLY-S&C ONLY-S&C&M=23-7-5-7=4
THOSE WHO TOOK COMPUTRERS ONLY =C-C&M ONLY-C&S ONLY-C&S&M=27-6-5-7=9
HENCE PROBABILITY OF HAVING THOSE WHO TOOK ONLY ONE SUBJECT=(5+4+9)/40=18/40=9/20


    What is the probability a student took exactly one of the three courses?

You may edit the question. Maybe convert formulae to the same formula notatio