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If two projectiles are launched at the same moment from...

This topic has 2 expert replies and 0 member replies

If two projectiles are launched at the same moment from...

Post Wed Mar 07, 2018 2:41 pm
If two projectiles are launched at the same moment from 1320 miles apart and travel directly towards each other at 480 miles per hour and 510 miles per hour, respectively, how many minutes will it take for them to meet?

A. 40
B. 44
C. 80
D. 88
E. 90

The OA is C.

I'm really confused by this PS question. Experts, any suggestion, please? Thanks in advance.

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mbawisdom Senior | Next Rank: 100 Posts Default Avatar
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Post Wed Mar 07, 2018 3:36 pm
LUANDATO wrote:
If two projectiles are launched at the same moment from 1320 miles apart and travel directly towards each other at 480 miles per hour and 510 miles per hour, respectively, how many minutes will it take for them to meet?

A. 40
B. 44
C. 80
D. 88
E. 90

The OA is C.

I'm really confused by this PS question. Experts, any suggestion, please? Thanks in advance.
Time = Distance / Speed

Here the speed we need to use is 990 (480 + 510) as the objects are travelling towards each other.

Time = 1320/990
Time = 1 1/3
Time = 80 min

Answer is C.

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GMAT/MBA Expert

Post Thu Mar 08, 2018 4:12 pm
Hi LUANDATO,

We're that two projectiles are launched at the same moment from 1320 miles apart and travel directly towards each other at 480 miles per hour and 510 miles per hour, respectively. We're asked for the number of minutes it will take for them to meet. The math behind this question can be done in number of different ways, depending on how you organize your work.

To start, it's worth noting that all of the answers are INTEGERS, so even though the numbers in this question might seem 'big'/'strange', they clearly end with a whole number once you do the necessary work (implying that there IS some sort of 'relationship' among these numbers). Since the two projectiles are traveling 480 miles/hour and 510 miles/hour, their COMBINED rate is 480 + 510 = 990 miles/hour. The total distance traveled is 1320 miles - and that distance is larger than the combined speed in miles/hour, so the total time is clearly MORE than 1 hour.

In that first hour, 990 miles are traveled, which would leave....
1320 - 990 = 330 miles to go

330/990 = an extra 1/3 of an hour to travel the remaining distance, so the total time is 1 1/3 hours = 1 hour 20 minutes

Final Answer: C

GMAT assassins aren't born, they're made,
Rich

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Contact Rich at Rich.C@empowergmat.com

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