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## McGraw-Hill Math Grade 3 Answer Key Chapter 12 Lesson 6 Finding a Perimeter or Unknown Side Length

**Solve**

**Find the perimeter.**

Question 1.

Answer:

16 cm

Question 2.

Answer:

15 ft

Explanation:

Perimeter of the triangle is sum of all the sides

That is 5 + 5 + 5 = 15

So, perimeter is 15 ft.

Question 3.

Answer:

4 m

Explanation:

Perimeter of the square is sum of all the sides

That is 1 + 1 + 1 + 1 = 4

So, perimeter is 4 m.

**Find the length of the unknown side.**

Question 4.

perimeter: 30 m

unknown side: ___________

Answer:

Unknown side = 10 m.

Explanation:

Given Perimeter = 30 m

Perimeter of the triangle is sum of all the sides

That is 10 + 10 + ? = 30

20 + ? = 30

30 – 20 = 10

So, unknown side = 10 m.

Question 5.

perimeter: 14 in

unknown side: _____________

Answer:

Unknown side = 4 in

Explanation:

Given perimeter = 14 in

Perimeter of a shape is sum of all the sides

2 + 3 + 2 + 3Â + ? = 14

10 + ? = 14

14 – 10 = 4

So, unknown side = 4 in.

Question 6.

perimeter: 16 ft

unknown side: _____________

Answer:

Unknown side = 8 ft

Explanation:

Given Perimeter = 16Â ft

Perimeter of the triangle is sum of all the sides

That is 2 + 6 + ? = 16

8 + ? = 16

16 – 8 = 8

So, unknown side = 8 ft.