A bird leaves its nest, and flies back and forth from...

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AAPL: Moderator; Posts: 2632; Joined: Sun Oct 29, 2017 2:08 pmFollowed by: 2 members

by AAPL » Sun Nov 19, 2017 2:59 pm

A bird leaves its nest, and flies back and forth from its nest to a nearby ditch to gather worms. The distance between the nest and the ditch is 200 meters. In one and a half hours, the bird manages to bring worms to its nest 15 times. What is the speed of the bird in kilometers per hour?

A) 1.
B) 2.
C) 4.
D) 5.
E) 6.

The OA is C.

Please, can any expert assist me with this PS question? I don't have it clear and I appreciate if any explain it for me. Thanks.

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Source: Beat The GMAT — Problem Solving | Sun Nov 19, 2017 2:59 pm

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ErikaPrepScholar: Legendary Member; Posts: 503; Joined: Thu Jul 20, 2017 9:03 amFollowed by: 15 members; Thanked: 86 times; GMAT Score:770

by ErikaPrepScholar » Mon Nov 20, 2017 10:13 am

To carry one worm to its nest, the bird must fly 200 meters out and 200 meters back, giving 400 meters in total. If the bird collected 15 worms, this gives a total of 6000 meters.

So the bird traveled 6000 meters in 1.5 hours. We need to now convert this into kilometers per hour $$\frac{6000\ meters}{1.5\ hours}=\ \frac{4000\ meters}{1\ hour}\cdot\frac{1\ kilometer}{1000\ meters}=\frac{4\ kilometers}{1\ hour}$$

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Jeff@TargetTestPrep: GMAT Instructor; Posts: 1462; Joined: Thu Apr 09, 2015 9:34 amFollowed by: 22 members; Location: New York, NY; Thanked: 39 times

by Jeff@TargetTestPrep » Wed Nov 22, 2017 11:17 am

AAPL wrote:A bird leaves its nest, and flies back and forth from its nest to a nearby ditch to gather worms. The distance between the nest and the ditch is 200 meters. In one and a half hours, the bird manages to bring worms to its nest 15 times. What is the speed of the bird in kilometers per hour?

A) 1.
B) 2.
C) 4.
D) 5.
E) 6.

The distance back and forth (i.e., the round-trip distance) is 400 meters. Going the round-trip distance 15 times is 15 x 400 = 6,000 meters, which is 6000/1000 = 6 kilometers.

Since this was done in 1.5 hours, the rate is 6/1.5 = 4 kilometers per hour.

Answer: C

Jeffrey Miller
Head of GMAT Instruction
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