The Earth Travels Around The Sun At A Speed Of Approximately 18.5 miles GMAT Problem Solving

Question: 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

“The earth travels around the sun at a speed of approximately 18.5 miles” - is a subject covered in the GMAT quantitative reasoning section. This question has been taken from the book “The official Guide for GMAT Review”. A student needs to be knowledgeable in a wide range of qualitative skills in order to successfully complete GMAT Problem Solving questions. There are 31 questions in the GMAT Quant section overall. Calculative mathematical problems must be solved in the GMAT quant topics' problem-solving section using appropriate mathematical skills.

Solutions and Explanation

Approach Solution : 1

This is a typical example of approximation

18.5 miles per second has to be converted to 18.5 miles per hour

One minute is 60 seconds and one hour is 60 minutes

Therefore one hour is 60*60=3600 seconds.

Thus the speed for one hour can be calculated by multiplying that with 3600.

18.5*3600 = 66,600

Correct Answer: (D)

Approach Solution : 2

The first is a nice rule that reads AB = (2A) (0.5B)

This technique can occasionally help us avoid doing some calculations.

Applying the rule, we get (18.5)(3600) = (37) (1800) [18.5 is multiplied by 2 to get 37 and 3600 is reduced to half to get 1800]

= (37)(18)(100) (100) [ 1800 is changed to be 18 x 100]

= (——6)(100) (100) [Since 7 x 8 = 56, we know that the units digit of 37 x 18 must be 6]

= —-600

Some number with a 600 at the end will be the answer.

Correct Answer: (D)

Approach Solution : 3

Let's address the problem by using 20 seconds as a base, then work out the 1.5 to subtract aside.

20 per second = 20*60 seconds = 1200 per minute

1200 per minute = 1200*60 minutes = 72000 per hour

1.5 per second = 1.5*60 seconds = 90 per minute

90 per minute = 90*60 minutes = 5400 per hour

72000-5400= 66,600

Correct Answer: (D)

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