The last rule lets you answer this question. If either type of rap is on sale (including used rap), then no soul is.
The contrapositive means that if any soul is on sale (including used soul) then no rap is on sale.
Here’s the same rule in graphical form:
This is all a complicated way of saying that used rap and used soul can’t be on sale at the same time.
That’s a problem, since we need four out of five of the used CDs to be on sale.
Since one of S or R is missing, everything else has to be in. The other three all have to be on sale.
So the CDs on sale are:
- Used opera
- Used pop
- Used jazz
- One of either used soul or used rap
Answers A and D say the same thing: used jazz isn’t on sale. We can’t have that. We’d only have three CDs.
B can’t be true either. If used opera isn’t on sale, we can only have three used CDs on sale.
E can’t be true. One of used rap and used soul isn’t on sale, but if they’re both not on sale, then we’ll only have three used CDs on sale.
C is CORRECT. Either used rap or used soul isn’t on sale, so this could be true.
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