Question

# The circumference of Earth is estimated to be 40,030 kilometers at the equator. Which of the following best approximates the diameter, in miles, of Earth's equator? (1 kilometer miles)

- 3,205 miles
- 5,541 miles
- 7,917 miles
- 13,004 miles

Hint:

**Hint:**

We are given the circumference of the earth at the equator. From that we find the diameter of the earth. This value will be in kilo meters. We simply need to convert this unit of measurement of length. We are given the conversion factor in the question itself. So we just need to use that to calculate the diameter in miles.

## The correct answer is: 7,917 miles

### Given,

Circumference of the earth at the equator = 40,030 kilomteres

The equator can be considered as a circle,

And the circumference of a circle = , where r is the radius of the circle.

As, diameter of a circle is twice the radius, that is, diameter = 2r ,

So we get

cicum ference diameter

Thus,

Putting the value of the circumference in the above equation

Using the calculator, we get

Thus, we get

Diameter of the earth 12741.94 kilometres

It is given that,

This is the unit conversion factor.

Thus, we have

= 7917.45

Thus, the correct option is C)

**Note:**

There are many other units of length which are often used. For example: inch, foot, yard, centimetre, parsec, lightyear, nanometre, etc. They measure anything between atoms to a galaxy.

Some relations between them are given by

1 kilometer = 39370.0787 inches = 3280.84 feet = 100000 centimetre

1 mile = 63357 inches = 5279.75 feet = 160926.94 centimetre

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