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# The earth travels around the sun at a speed of approximately 18.5 mile

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Intern
Joined: 05 Aug 2015
Posts: 22
The earth travels around the sun at a speed of approximately 18.5 mile  [#permalink]

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30 Aug 2015, 01:59
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Difficulty:

15% (low)

Question Stats:

80% (01:18) correct 20% (01:23) wrong based on 244 sessions

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The earth travels around the sun at a speed of approximately 18.5 miles per second. The approximate speed is how many miles per hour?

(A) 1,080
(B) 1,160
(C) 64,800
(D) 66,600
(E) 3,996,000
Intern
Joined: 05 Aug 2015
Posts: 22
Re: The earth travels around the sun at a speed of approximately 18.5 mile  [#permalink]

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30 Aug 2015, 02:10
18.5miles/second x 60seconds/minute x 60minutes/hour = 18.5(60)(60) = 18.5(3600) = 185(360). Long multiplication to solve.

Is there a quicker way?

My initial method, as I try to avoid long multiplication was:
185 x 100 = 18500
20,000 x 3 = 60,000 - 4,500 = 55,500
185 x 60 = ~9300 (185x50)+ 1850 (185x10) = 11,500
45,000 + 11,000 = 66,000

However this is somewhat in the middle of C and D and therefore prone to error. I was even a little more liberal in my rounding while doing it the first time which placed my answer right in the middle of the two. Doing this also takes a toll on my brainpower and I think I should avoid it as it tires me out a bit, which is bad in the exam. It also ended up taking as long as a quickly done long multiplication.

Would you guys suggest just going for long multiplication? Or do you have a nicer, fast and accurate way to go through this?
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Re: The earth travels around the sun at a speed of approximately 18.5 mile  [#permalink]

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30 Aug 2015, 03:38
3
1
Matthias15 wrote:
The earth travels around the sun at a speed of approximately 18.5 miles per second. The approximate speed is how many miles per hour?

(A) 1,080
(B) 1,160
(C) 64,800
(D) 66,600
(E) 3,996,000

This is a classic case of approximations as the options are too widespread.

18.5 mps to 18.5 mph with 1 h = 3600 seconds.

Thus 18.5 mps = 18.5*3600 = a bit more than 18*3600 = a bit more than 18*18*200 = a bit more than 324*2*100 = a bit more than 64800 . So eliminate C and mark D is the correct answer.

You need to remember squares from 1 to 20 for GMAT.

Hope this helps.
Math Expert
Joined: 02 Sep 2009
Posts: 50627
Re: The earth travels around the sun at a speed of approximately 18.5 mile  [#permalink]

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30 Aug 2015, 04:20
Matthias15 wrote:
The earth travels around the sun at a speed of approximately 18.5 miles per second. The approximate speed is how many miles per hour?

(A) 1,080
(B) 1,160
(C) 64,800
(D) 66,600
(E) 3,996,000

Similar question to practice: the-earth-travels-around-the-sun-at-an-approximate-speed-of-20-miles-p-189377.html

Check other Conversion problems to practice in Special Questions Directory.
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Re: The earth travels around the sun at a speed of approximately 18.5 mile  [#permalink]

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30 Aug 2015, 05:09
Engr2012 wrote:
Matthias15 wrote:
The earth travels around the sun at a speed of approximately 18.5 miles per second. The approximate speed is how many miles per hour?

(A) 1,080
(B) 1,160
(C) 64,800
(D) 66,600
(E) 3,996,000

This is a classic case of approximations as the options are too widespread.

18.5 mps to 18.5 mph with 1 h = 3600 seconds.

Thus 18.5 mps = 18.5*3600 = a bit more than 18*3600 = a bit more than 18*18*200 = a bit more than 324*2*100 = a bit more than 64800 . So eliminate C and mark D is the correct answer.

You need to remember squares from 1 to 20 for GMAT.

Hope this helps.

This is great! I'm going to practice this method. However I could still see a problem if the answers were, say, 65,000 and 66,600. I guess in this worst case scenario you could go back and calculate that 0.5 x 3600 and add it, which doesn't take that long.
Intern
Joined: 24 Aug 2017
Posts: 3
Re: The earth travels around the sun at a speed of approximately 18.5 mile  [#permalink]

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09 Sep 2017, 04:05
1
1
In 1 second the Sun travels approx 18.5 miles,i.e.
1S= 18.5
1min= 18.5×60
1hr= 18.5×60×60 = 66600

Posted from my mobile device
GMATH Teacher
Status: GMATH founder
Joined: 12 Oct 2010
Posts: 478
The earth travels around the sun at a speed of approximately 18.5 mile  [#permalink]

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11 Sep 2018, 10:10
1
Matthias15 wrote:
The earth travels around the sun at a speed of approximately 18.5 miles per second. The approximate speed is how many miles per hour?

(A) 1,080
(B) 1,160
(C) 64,800
(D) 66,600
(E) 3,996,000

Trivial application of the UNITS CONTROL, one of our method´s most powerful techniques!

$$?\,\,\, = \,\,\,\frac{{18.5\,\,{\text{miles}}}}{{1\,\,{\text{s}}}}\,\,\,\left( {\frac{{60\,\,{\text{s}}}}{{1\,\,{\text{minute}}}}\,\,\begin{array}{*{20}{c}} \nearrow \\ \nearrow \end{array}} \right)\,\,\,\,\left( {\frac{{60\,\,{\text{minutes}}}}{{1\,\,{\text{h}}}}\,\,\begin{array}{*{20}{c}} \nearrow \\ \nearrow \end{array}} \right)\,\,\,\, = \,\,\frac{{37}}{2} \cdot 36 \cdot 100 = 37 \cdot 18 \cdot 100 = 66,600\,\,\,\left[ {{\text{mph}}} \right]$$

Obs.: arrows indicate licit converters.

This solution follows the notations and rationale taught in the GMATH method.

Regards,
fskilnik.
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Posts: 3122
Re: The earth travels around the sun at a speed of approximately 18.5 mile  [#permalink]

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11 Sep 2018, 10:20
1
Top Contributor
Another way to deal with calculating (18.5)(3600) is to use the answer choices to our advantage.

First off, there's a nice rule that says: AB = (2A)(0.5B)
This strategy (which is covered in the video below) can sometimes save us some calculations.

When we apply the rule, (18.5)(3600) = (37)(1800) [I doubled 18.5 to get 37, and I halved 3600 to get 1800 ]
= (37)(18)(100) [I rewrote 1800 as 18 x 100]
= (----6)(100) [We know that the units digit of 37 x 18 must be 6, since 7 x 8 = 56]
= ---600 [some number that ends with 600]

A. 1,080
B. 1,160
C. 64,800
D. 66,600 BINGO!!
E. 3,996,000

RELATED VIDEO FROM OUR COURSE

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Re: The earth travels around the sun at a speed of approximately 18.5 mile  [#permalink]

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12 Sep 2018, 17:26
Matthias15 wrote:
The earth travels around the sun at a speed of approximately 18.5 miles per second. The approximate speed is how many miles per hour?

(A) 1,080
(B) 1,160
(C) 64,800
(D) 66,600
(E) 3,996,000

Since 1 second = 1/3600 hours, the rate in miles per hour is:

18.5/(1/3600) = 18.5 x 3600 = 66,600

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Re: The earth travels around the sun at a speed of approximately 18.5 mile &nbs [#permalink] 12 Sep 2018, 17:26
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