# Carpentry & Building Construction

## Math Activities :

### Circumference of a Circle

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Carpenters often have to find the distance around the outside of a circle. The distance around a circle is its circumference. To find the circumference of a circle, multiply the diameter of the circle times pi. The value of pi is approximately 3.1416. Pi is written in equations as π.

Since the diameter of a circle is equal to twice its radius, another way to find the circumference is to use the formula, 2πr, or two times pi times the radius.

 Terms, Symbols, & Abbreviationscircumference – the distance around a circlediameter – the length of a straight line through the center of a circleradius – one-half the distance of the diameterpi, or π – the ratio of the circumference of a circle to its diameter, approximately 3.1416

Practice Exercise

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Find the circumference of the circle when the diameter is 12''.
 Step 1 The formula is C = πd. Step 2 Insert the known values. C = 3.1416 × 12'' Step 3 C = 37.6992''
Find the circumference when the radius is 6''.
 Step 1 The formula is C = 2πr. Step 2 Insert the known values. C = 2 × 3.1416 × 6'' Step 3 C= 37.6992''

Problem Exercises

For each problem, round the answer to the nearest hundredth.

 1 Find the circumference of a circle whose diameter is 8'. A) 8.00' B) 16.00' C) 25.13' D) 50.17' 2 Find the circumference of a circle whose radius is 15'. A) 47.12' B) 94.25' C) 30.00' D) 15.00' 3 The circumference of a circle whose radius is 6' and diameter is 12' is A) 37.70'. B) 72.00' C) 56.55'. D) 226.51'. 4 A carpenter will build a platform around a tree whose circumference is 24''. She wants to leave 6'' of clearance between the platform and the tree. Find the diameter of the opening needed for the tree. A) 7.64'' B) 13.64'' C) 30.00'' D) 19.64'' 5 A deck will be built around a 14' diameter swimming pool. What is the circumference of the deck at the pool’s edge? A) 4.45' B) 43.98' C) 88.08' D) 528.48'