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Step-3

Title: Circumference of a circle

Grade: 7-a Lesson: S1-L3

Explanation:

Step	Type	Explanation	Answer
1	Problem	The diameter of the circle is 42m. Find the circumference.
2	Formula:	Radius of a circle.	r = \$\frac(d)(2)\$
3	Step	Substitute 42 for d.	r = \$\frac(42)(2)\$
4	Step	Divide.	r = \${\cancel{42}^21}/{\cancel{2}^1}\$ r = 21
5	Formula:	Circumference of a circle.	C = \$2 \pi r\$
6	Step	Substitute \$22/7\$ for \$pi\$ and 21 for r.	C = \$2\times\frac(22)(7)\times21\$
7	Step	Cancel out common factor.	C = \$2\times22/\cancel{7}^1 \times \cancel{21}^3\$
8	Step	Multiply.	C = \$2\times(22)\times3\$ c = 132
9		Answer	The circumference is \$132m\$.

Step

Type

Explanation

Answer

Problem

The diameter of the circle is 42m. Find the circumference.

Formula:

Radius of a circle.

r = \$\frac(d)(2)\$

Step

Substitute 42 for d.

r = \$\frac(42)(2)\$

Step

Divide.

r = \${\cancel{42}^21}/{\cancel{2}^1}\$
r = 21

Formula:

Circumference of a circle.

C = \$2 \pi r\$

Step

Substitute \$22/7\$ for \$pi\$ and 21 for r.

C = \$2\times\frac(22)(7)\times21\$

Step

Cancel out common factor.

C = \$2\times22/\cancel{7}^1 \times \cancel{21}^3\$

Step

Multiply.

C = \$2\times(22)\times3\$
c = 132

Answer

The circumference is \$132m\$.