During the past month, a disease control center tested X individuals for two viruses. If 1/3 of those tested had virus C and, of those with virus C, 1/5 also had virus D, how many individuals did not have both virus C and D?
E. 4 / 5
The number of individuals that had virus C is 1/3 of X, or X/3.
The number of individuals that also had virus D is 1/5 of the number that had virus C.
Thus (1/5)C= (1/5)(X/3) = X/15.
If X/15 of the X individuals have virus C and D, then X - (X/15) did not have both virus C and D.
Neither C or D: X - (X/15) = 14X/15.
The correct answer is D.
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