IXL - Perimeters of similar figures (Geometry practice)

The figures below are similar. The labeled sides are corresponding.

8 cm

3 cm

What is the ratio of the perimeter of the larger triangle to the perimeter of the smaller triangle?

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

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question

The figures below are similar. The labeled sides are corresponding.

5 in

3 in

What is the ratio of the perimeter of the larger triangle to the perimeter of the smaller triangle?

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 similar shapes:

where
a
b
is
the
ratio
of
the
corresponding
side
lengths,
and
P1
P2
is
the
ratio
of
the
perimeters.

In other words, the ratio of the corresponding side lengths is the same as the ratio of the perimeters.

solution

Find the ratio of the corresponding side lengths.

Find the ratio of the perimeters.

Use these two ratios to set up a proportion.

Write the fraction as a ratio.

→

5:3

The ratio of the larger triangle's perimeter to the smaller triangle's perimeter is 5:3.

Looking for more? Try these:

Lesson: Similarity

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Teacher tools

Work it out

Not feeling ready yet? These can help:

M.1Ratios in similar figures

S.1Perimeter

Lesson: Similarity

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