On a certain trip, a cyclist averaged 20 miles per hour for

Hi All,

Based on the way that the answer choices are written, there is a minor math "shortcut" built into this question that you can take advantage of to avoid the last couple of calculations.

Bunuel's calculations are spot-on, so I won't rehash any of that here. Instead, I'll jump straight to the shortcut:

Once you've determined that the return trip takes MORE than 2 hours, since the distance is 30 miles, the average speed for the return trip must be LESS than 15 miles/hour. Here's why:

Using the Distance Formula as reference, we know that if the time was EXACTLY 2 hours, the rate would be 15 miles/hour...

Distance = (Rate)(Time)
30 mi = (15 mph)(2hours)

By increasing the Time, the rate will be decreased (that's the only way that the distance will continue to = 30).

There's only one answer that fits this pattern (and we don't even need to calculate it).

Final Answer:

GMAT assassins aren't born, they're made,
Rich