IXL - Areas of similar circles (Geometry practice)

The figures below are similar.

7 ft

3 ft

What is the ratio of the area of the larger circle to the area of the smaller circle?

Write your answer as the ratio of two whole numbers separated by a colon (for example, 2:3).

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Learn with an example

question

The figures below are similar.

8 yd

2 yd

What is the ratio of the area of the larger circle to the area of the smaller circle?

Write your answer as the ratio of two whole numbers separated by a colon (for example, 2:3).

key idea

The following proportion applies to all circles:

where
a
b
is
the
ratio
of
the
diameters,
and
A1
A2
is
the
ratio
of
the
areas.

solution

Find the square of the ratio of the diameters.

Find the ratio of the areas.

Use these two ratios to set up a proportion.

Write the fraction as a ratio.

→

16:1

The ratio of the larger circle's area to the smaller circle's area is 16:1.

Looking for more? Try this:

Lesson: Similarity

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Area of circles

Lesson: Similarity

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