Hi NandishSS,
This question is all about 'unit conversions.' We're told that a bird flies at an average speed of 18 meters/second. We're asked if the distance traveled by the bird was LESS than 21 kilometers. This is a YES/NO question.
Before dealing with the 2 Facts, let's 'rewrite' the question...
18 m/second =
1080 m/minute =
1.08 km/minute
Using this measure should make it easier to use the given information in the two Facts to answer the question.
1) It took the bird less than 20 minutes to fly across the lake.
This Fact gives us an 'upper limit' to how far the bird COULD have flown...
20 minutes * 1.08 km/minute = (20)(1.08) = 21.6 km
So we know that bird flew LESS than 21.6 km
IF...
the bird flew 21.5 km, then the answer to the question is NO
the bird flew 19 km, then the answer to the question is YES
Fact 1 is INSUFFICIENT
2) It took the bird less than 0.4 hour to fly across the lake.
.4 hours = (.4)(60 minutes) = 24 minutes
Based on the information in Fact 1, we determined that after less than 20 minutes of flight, the answer could be YES or NO. Here, we're told that it was less than 24 minutes of flight - which creates the same 2 possibilities that exist in Fact 1. The answer could be YES or NO.
Fact 2 is INSUFFICIENT
Combined, there's no more work to be done. We have proof that the answer changes based on the number of minutes that were actually flown and that there are two different possible answers.
Combined, INSUFFICIENT
Final Answer: E
GMAT assassins aren't born, they're made,
Rich
