McGrawHill questions are terrible. It's just too easy to eliminate based purely on answer choices. But let's do it anyway for practice. If you look inside the parenthesis, you see 5/8  4. Don't just robotically start crossmultiplying: think to yourself, how can I eliminate answers? 5/8  4 will get us a negative number right? This negative is then multiplied by 3/5, which is a positive, which means we'll get a negative number. So C, D, and E are out.
A and B are pretty different in size, so we can use that. Rather than actually doing the math, let's eyeball things. Let's pretend 5/8 is 1/2. So 1/2  4 is 3.5. If we multiply that by 3/5, well basically I don't want to, so let's pretend 3/5 is about 1/2 again. So then what's 1/2 of 3.5? It's 1.75, which is in the ballpark of A, and nowhere near B. So it's A. We did some pretty rough estimating, but that was ok in this case since the answers were so far apart. But if they'd been pretty close, which I think is more likely on the GRE, we would've had to actually do the math.
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