Last Updated on May 10, 2023
GMAT OFFICIAL GUIDE DS
Solution:
We are given that Joan accurately divided her estimated distance by her estimated average speed to obtain an estimate for the time, in hours, that the trip would take. We must determine whether her estimate was within 0.5 hour of the actual time that the trip took.
Statement One Alone:
Joan’s estimate for the distance was within 5 miles of the actual distance.
Since we are not given any information about the time, statement one alone is not sufficient to answer the question. We can eliminate answer choices A and D.
Statement Two Alone:
Joan’s estimate for her average speed was within 10 miles per hour of her actual average speed.
Since we are not given any information about the average speed, statement two alone is not sufficient to answer the question. We can eliminate answer choices A and D.
Statements One and Two Together:
Using statements one and two together, we still do not have enough information to answer the question. Let’s say Joan’s actual distance was 100 miles and her actual average speed was 20 mph; her actual time would be 100/20 = 5 hours.
Let’s now say in one scenario her estimated distance was 105 miles and her estimated average speed was 10 mph; her estimated time would be 105/10 = 10.5 hours. 10.5 hours is not within 0.5 or an hour of her actual time of 5 hours.
However, in another scenario let’s say her estimate for distance and average speed matched her actual distance and actual average speed. In that case, her estimated time would be within 0.5 hours of her actual time. Thus, statements one and two are not enough information to answer the question.
Answer: E
