Scott Woodbury-Stewart

GMAT OFFICIAL GUIDE DS – A conveyor belt moves bottles at a constant speed of 120 centimeters per second…

A conveyor belt moves bottles at a constant speed of 120 centimeters per second…

Solution:

We are given that a conveyer belt moves at a constant speed of 120 centimeters per second. We must determine whether the distance the conveyer belt moves is less than 90 meters.

Thus, the question becomes “is distance < 90 meters?”. However, we are only given the speed of the conveyor belt in the stem and a time is given in each of the two statements. It’s better to use the fact that distance = rate x time or r x t = d to create the following question:

Is r x t <90 meters ?

Since we know that the rate is 120 centimeters per second, we can substitute that in for the rate. However, then we also have to convert 90 meters to 9,000 centimeters to keep the units for distance the same. So we have:

Is (120 cm/sec) x t < 9,000 cm ?

Is t < (9,000/120) sec ?

Is t < 75 sec ?

Finally we can convert our time in seconds to minutes by dividing by 60, so we have:

Is t <75/60 min ?

Is t < 5/4 min ?

Is t < 1.25 min ?

Statement One Alone: 

It takes the conveyer belt less than 1.2 minutes to move the bottle from the loading dock to the unloading dock.

Using the information in statement one we know that t < 1.2 minutes; thus, t < 1.25 minutes. Statement one alone is sufficient to answer the question. We can eliminate answer choices B, C, and E.

Statement Two Alone: 

It takes the conveyer belt more than 1.1 minutes to move the bottle from the loading dock to the unloading dock.

Using the information in statement two, we see that the time to move the bottle could be less than 1.25 minutes (for example, t = 1.2 minutes) or greater than 1.25 minutes (for example, t = 1.3 minutes). Thus, the information in statement two is not sufficient to answer the question.

Answer: A 

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