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# A space shuttle orbits the earth at about 8 kilometers per second. Thi

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Posts: 39626
A space shuttle orbits the earth at about 8 kilometers per second. Thi [#permalink]

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16 Apr 2015, 05:09
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A space shuttle orbits the earth at about 8 kilometers per second. This speed is equal to how many kilometers per hour?

(A) 480
(B) 2,880
(C) 4,800
(D) 28,800
(E) 48,000

Kudos for a correct solution.
[Reveal] Spoiler: OA

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Re: A space shuttle orbits the earth at about 8 kilometers per second. Thi [#permalink]

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16 Apr 2015, 05:13
Bunuel wrote:
A space shuttle orbits the earth at about 8 kilometers per second. This speed is equal to how many kilometers per hour?

(A) 480
(B) 2,880
(C) 4,800
(D) 28,800
(E) 48,000

Kudos for a correct solution.

Seconds in 1 hours:
60s in 1 min
60 min in 1 hr
60*60=3600 sec in 1 hr

8*3600=28,800

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Re: A space shuttle orbits the earth at about 8 kilometers per second. Thi [#permalink]

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16 Apr 2015, 10:17
1
KUDOS
Conerting from Sec to Hrs : multiply by 3600,
=> 8km/s = 8 *3600 km/hr
=> 28800 km/hr.
D.
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Kudos!!

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Re: A space shuttle orbits the earth at about 8 kilometers per second. Thi [#permalink]

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16 Apr 2015, 19:27
1
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(8 km/s) * (60 sec/min) * (60 min/hr)
= 28,800 km/hr

Math Expert
Joined: 02 Sep 2009
Posts: 39626
Re: A space shuttle orbits the earth at about 8 kilometers per second. Thi [#permalink]

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20 Apr 2015, 05:23
Bunuel wrote:
A space shuttle orbits the earth at about 8 kilometers per second. This speed is equal to how many kilometers per hour?

(A) 480
(B) 2,880
(C) 4,800
(D) 28,800
(E) 48,000

Kudos for a correct solution.

VERITAS PREP OFFICIAL SOLUTION

This is the type of question that can bait you into time-consuming calculations, whereas a shrewd test taker can gain valuable time by recognizing that this question is simply asking you to calculate a certain number by 60, and then multiplying it by 60 again (let’s do the time warp!). Even if a question asks you to change one unit into another, you can always do it step by step or all in one shot. There are many ways to solve this, but let’s begin with the detailed process so we make sure we don’t make any mistakes.

If the space shuttle orbits the earth at 8 kilometers per second (you can replace this word by miles if you’re more comfortable), then how many kilometers will it cover in one minute? We can simply multiply 8 by 60 to get 480 kilometers/minute. This is the number in answer choice A, but it is not the correct answer as we’ve only covered a single minute, or about 1.67% of the hour. (There’s still a lot of spinning to go!). If we take the 480 km/minute and multiply it by 60 minutes, we will get to the number of kilometers /hour. 480 x 60 is not obvious, but you ignore the 0’s so it boils down to 48 x 6. Doing this longhand, we can get to 288, and then add back in the two zeros for a total of 28,800. This is answer choice D and the correct answer to this question.

If you followed that strategy, you would get the right answer, but you would miss many opportunities for shortcuts. One of the most glaring shortcuts is to forgo the two-step process and simply multiply the initial speed of 8 km/second by 3,600. This is 60 x 60, and represents the number of seconds in an hour. Since 60 is a number that shows up so frequently on the GMAT, it’s worth knowing that the square of 60 is 3,600 as you may be asked to convert from hour to second and vice versa. Multiplying 8 by 3,600 will also get you to 28,800 in one operation instead of two.

There are also multiple other ways to get the right answer here. One hybrid solution that is pretty intuitive is to multiply 8 kilometers/second by 60 to get 480 kilometers/minute, as we did in the very first step. From there you know you need to multiply 480 by 60 to get the speed per hour, but your trap options are 480 x 10 and 480 x 100, both of which are clearly incorrect at a cursory glance. By order of magnitude, you can again determine that the correct choice must be D.
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Re: A space shuttle orbits the earth at about 8 kilometers per second. Thi [#permalink]

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19 Jun 2017, 11:26
Bunuel wrote:
A space shuttle orbits the earth at about 8 kilometers per second. This speed is equal to how many kilometers per hour?

(A) 480
(B) 2,880
(C) 4,800
(D) 28,800
(E) 48,000

Kudos for a correct solution.

We can start with conversion factors- though it's not necessary once you've practiced the concept enough

[8 km /1s] x [60/ 60] = 8 x 60 /1min x 60/60 = 8(60)(60) /1 hour = 28800

Thus
"D"
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A space shuttle orbits the earth at about 8 kilometers per second. Thi [#permalink]

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19 Jun 2017, 11:42
We need to find out the value of 8 km/sec in km/hour?

Since 1 hour has 3600 seconds, 1 km/sec would be 3600 km/hour
Hence, 8 km/sec translates to around 28800 km/hour(Option D)
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Re: A space shuttle orbits the earth at about 8 kilometers per second. Thi [#permalink]

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19 Jun 2017, 16:39
Top Contributor
Bunuel wrote:
A space shuttle orbits the earth at about 8 kilometers per second. This speed is equal to how many kilometers per hour?

(A) 480
(B) 2,880
(C) 4,800
(D) 28,800
(E) 48,000

Kudos for a correct solution.

We can solve this using equivalent ratios

1 hour = 3600 seconds

So, let's use equivalent ratio to compare kilometers/seconds
We get: 8/1 = x/3600
Cross multiply: (8)(3600) = (x)(1)
Simplify: (8)(3600) = x
Since (8)(4000) = 32,000, we can conclude that (8)(3600) is a little bit less than 32,000

[Reveal] Spoiler:
D

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Re: A space shuttle orbits the earth at about 8 kilometers per second. Thi [#permalink]

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20 Jun 2017, 08:12
Bunuel wrote:
A space shuttle orbits the earth at about 8 kilometers per second. This speed is equal to how many kilometers per hour?

(A) 480
(B) 2,880
(C) 4,800
(D) 28,800
(E) 48,000

Kudos for a correct solution.

$$8 \ km/sec$$ * 60 = $$480 \ km/min$$

$$480 \ km/sec$$ * 60 = $$28800 \ km/Hr$$

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Re: A space shuttle orbits the earth at about 8 kilometers per second. Thi   [#permalink] 20 Jun 2017, 08:12
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