3. The ratio of the width to the length of a rectangle is 4:5. If the area of the rectangle is 500 square centimeters, what is the length of the rectangle? 5 centimeters
9 centimeters
20 centimeters
25 centimeters

Step-by-step explanation:

Ratio 4:5 means:

width: W = 4x

length: L = 5x

Area of rectangle:  A = W×L

Therefore:

              500 = 4x×5x

               500 = 20x²

               50 = 2x²

                x² = 25

                x = 5

W = 4×5 = 20 cm

L = 5×5 = 25 cm

A multiple of  

5

Explanation:

Percent means "per hundred", expressing a proportion.

The proportion of boys in the class is:

40

100

=

2

⋅

20

5

⋅

20

=

2

5

In other words, for every  

5

students in the class,  

2

are boys and  

3

are girls.

In order that the figure  

40

%

be exact, the number of students must be a multiple of  

5

.

Then the number of boys will be the corresponding multiple of  

2

and the number of girls the corresponding multiple of  

3

.

That is about as much as we can deduce from the question as given.