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OG PS28

by jscpba » Tue Jan 11, 2011 9:30 am
I am not totally understanding the OG explanation to arrive at this solution.

The average distance between the Un and a certain planet is approximately 2.3*10^14 inches. Which of the following is closest to the average distance between the Sun and the planet, in kilometers? (1 kilometer is approximately 3.9*10^4 inches)

a. 7.1*10^8
b. 5.9*10^9
c. 1.6*10^10
d. 1.6*10^11
e. 5.9*10^11

Please explain why you take the steps you do. All help is appreciated in advance!
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by Night reader » Tue Jan 11, 2011 9:38 am
jscpba wrote:I am not totally understanding the OG explanation to arrive at this solution.

The average distance between the Un and a certain planet is approximately 2.3*10^14 inches. Which of the following is closest to the average distance between the Sun and the planet, in kilometers? (1 kilometer is approximately 3.9*10^4 inches)

a. 7.1*10^8
b. 5.9*10^9
c. 1.6*10^10
d. 1.6*10^11
e. 5.9*10^11

Please explain why you take the steps you do. All help is appreciated in advance!
Call distance in km. x, simple calculation gives us x=(2.3*10^14)/(3.9*10^4)= (23*10^[14-1]) / (39*10^[4-1])= (23/39)*10^10,
23 is prime number, so instead consider 24/40=3/5=~ 0.6 OR 6/10

(6/10)*10^10= 6*10^9

the closest answer is b.
Last edited by Night reader on Tue Jan 11, 2011 9:39 am, edited 1 time in total.
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by shashank.ism » Tue Jan 11, 2011 9:39 am
jscpba wrote:I am not totally understanding the OG explanation to arrive at this solution.

The average distance between the Un and a certain planet is approximately 2.3*10^14 inches. Which of the following is closest to the average distance between the Sun and the planet, in kilometers? (1 kilometer is approximately 3.9*10^4 inches)

a. 7.1*10^8
b. 5.9*10^9
c. 1.6*10^10
d. 1.6*10^11
e. 5.9*10^11

Please explain why you take the steps you do. All help is appreciated in advance!
Distance between sun and planet = 2.3 x 10^14 inches
1 km = 3.9 x 10^4 inches
--> 1 inch = 1/(3.9 x 10^4) km

so distance between the Sun and the planet, in kilometers = (2.3 x 10^14) x 1 inch
= [(2.3 x 10^14) x 1/(3.9 x 10^4)] km
= 2.3/3.9 x 10^10 km
~ 0.6 x 10^10 km
~6 x 10^9 km

so Correct ans will be [spoiler]B = 5.9*10^9[/spoiler]

I think its quite easy and you can do it in 30 seconds.... :).. Ask if u have further querry ..
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by Anurag@Gurome » Tue Jan 11, 2011 9:41 am
The average distance between the Un and a certain planet is approximately 2.3*10^14 inches. Which of the following is closest to the average distance between the Sun and the planet, in kilometers? (1 kilometer is approximately 3.9*10^4 inches)

a. 7.1*10^8
b. 5.9*10^9
c. 1.6*10^10
d. 1.6*10^11
e. 5.9*10^11
We have to find 2.3*10^14 inches = how much in kilometers...

Now, 3.9*10^4 inches = 1 kilometer
=> 1 inch = 1/(3.9*10^4) kilometers
=> 2.3*10^14 inches = (2.3*10^14)/(3.9*10^4) kilometers

Now, (2.3*10^14)/(3.9*10^4) = (2.3*10^10)/(3.9) ≈ (2.3*10^10)/(4) = (0.575*10^10) = (5.75*10^9)

The correct answer is B.
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by GMATGuruNY » Tue Jan 11, 2011 9:42 am
jscpba wrote:I am not totally understanding the OG explanation to arrive at this solution.

The average distance between the Un and a certain planet is approximately 2.3*10^14 inches. Which of the following is closest to the average distance between the Sun and the planet, in kilometers? (1 kilometer is approximately 3.9*10^4 inches)

a. 7.1*10^8
b. 5.9*10^9
c. 1.6*10^10
d. 1.6*10^11
e. 5.9*10^11

Please explain why you take the steps you do. All help is appreciated in advance!
Set up the following proportion:
(3.9*10^4 inches)/1 kilometer = (2.3*10^14 inches)/x kilometers

Solve for x:
x = (2.3*10^14)/(3.9*10^4)

Since the answer choices are spread out, ballpark:
x ≈ (2*10^14)/(4*10^4)

Divide 2 by 4, subtract the exponents:
x ≈ .5*10^10
x ≈ 5*10^9

The correct answer is B.
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by shashank.ism » Tue Jan 11, 2011 9:54 am
Its quite easy problem.... :)
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by jscpba » Tue Jan 11, 2011 12:24 pm
Wow I wasn't thinking clearly when I posted this. Thanks for the help, it is indeed an easy problem you thanks for pointing that out.
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