1. ## Which Number?

In which number is 72 meters per hour expressed as kilometer per hour?

(a) 7.2 x 10^(-2)

(b) 7.2 x 10^(2)

(c) 7.2 x 10^(-3)

(d) 7.2 x 10^(3)

Although it is multiple choice, I want to know how to find the answer.

2. Originally Posted by magentarita
In which number is 72 meters per hour expressed as kilometer per hour?

(a) 7.2 x 10^(-2)

(b) 7.2 x 10^(2)

(c) 7.2 x 10^(-3)

(d) 7.2 x 10^(3)

Although it is multiple choice, I want to know how to find the answer.
In general here is the idea

If you have some number with units like this

$a\frac{meters}{hour}$

Note the conversion factor $1000meters= 1 kilometer$

$a\frac{meters}{hour}\cdot \frac{1 kilometer}{1000 meters}=a\frac{kilometers}{1000hour}$

3. Originally Posted by magentarita
Although it is multiple choice, I want to know how to find the answer.
To learn how to convert between metric units, try here.

To learn how to convert decimal values into scientific notation, try here.

4. Originally Posted by magentarita
In which number is 72 meters per hour expressed as kilometer per hour?

(a) 7.2 x 10^(-2)

(b) 7.2 x 10^(2)

(c) 7.2 x 10^(-3)

(d) 7.2 x 10^(3)

Although it is multiple choice, I want to know how to find the answer.
You want to express 72 meters as so many parts of a kilometer.

Since there are 1000 meters in a kilometer you will need to divide 72 by 1000 to get the meters into kilometers. Then convert it to scientific notation.

Actually the easy way is to shift the decimal point in the choices given:

Code:

(a) 7.2 x 10^(-2) =   0.0720
(b) 7.2 x 10^(2)  = 720.0000
(c) 7.2 x 10^(-3) =   0.0072
(d) 7.2 x 10^(3)  =7200.0000
With minimal thinking you can determine the correct answer.