9 - 760+: Using the Answers in a PS Question to Your Advantage

By richc On Oct 26, 2021 In  Quant Verbal IR Study Plans General GMAT MBA Advice & Tips 

In a couple of prior posts in this thread, we’ve discussed how to taking advantage of the answer choices (by TESTing THE ANSWERS or by thinking about what the answers choices 'mean') can be a really fast and easy way to get to the correct answer in certain Quant questions. Beyond using the answers and doing the straight-forward arithmetic though, you will sometimes be given a HUGE ‘hint’ from the GMAT question writers – the answer choices themselves will be designed in such a way that you can avoid doing a lot of math altogether. One of the ‘keys’ to spotting (and using) those shortcuts is to be on the lookout for quirky clues in the wording of the prompt.
Consider the following question:
A motorist averaged 40 miles per hour on his way to work. He averaged 70 miles per hour on his way home along the same route. Which of the following is the closest to his average speed for the round trip?
A) 40
B) 51
C) 55
D) 59
E) 59.5
If you’d like to approach this question without any hints to start, then you absolutely should – and you can post your solution here:
Now, let’s discuss the shortcut I alluded to earlier…
This prompt is a fairly common 'design' for a Weighted Average question. Here, a motorist travels a certain distance at one speed, then travels back - the SAME distance - at a different speed. We're asked for the AVERAGE SPEED for the entire trip.

One of the key elements to these types of questions is that the answer will be closer to the slower speed than to the faster speed. The exact 'middle' between 40 and 70 is 55, BUT since the motorist spends MORE time driving 40 mph, the average would have to be closer to 40 (while not being 40 exactly). There's only one answer that 'fits'...
The 'takeaway' from all of this: when approaching GMAT questions, the best Test Takers use ALL of the information that they've been given - including whatever is in the five answer choices.
Tomorrow, I’ll provide 3 additional prompts that you can solve by taking advantage of the answer choices.
GMAT assassins aren’t born, they’re made,
If you have any questions about anything in this thread, then you can feel free to contact me directly via email (at [email protected])

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