Carpentry & Building Construction © 2004

Math Activities :

Self-Check Math Activity 14

Working with Percents

Carpenters use percents for finding waste allowances, overhead costs, and other expenses related to a job.

Percents are easy to work with if you remember these formulas:

Percent = Part ÷ Whole

Part = Percent × Whole

Whole = Part ÷ Percent

Terms, Symbols, & Abbreviations
percent - by the hundred

Practice Exercise

A store offers a $15 rebate on a $250 tool. Another store offers an 8% discount on this tool. Which is the better deal?
Step 1	$15 is the Part and $250 is the Whole. You need to find the Percent.
	Percent = Part ÷ Whole
	Percent = 15 ÷ 250
	Percent = 0.06
Step 2	Convert the decimal to a percent
	0.06 = 6%
Thus $15 is only 6% of $250. You will save more at the second store, which offered an 8% discount.

Another way to solve the same problem is to find out how much 8% of $250 is.
Step 1 The Percent is 8, and $250 is the Whole. You need to find the Part. Start by
converting
8% to a decimal.
8% = 0.08
Step 2 Apply the formula.
Part = Percent × Whole
Part = 0.08 × 250
Part = 20
An 8% discount on a $250 tool is equal to $20.

Problem Exercises


1.	For every $100 spent in materials, a supplier will provide a $20 discount. What is the percent of the discount?
		A)	$20
		B)	20%
		C)	100/20%
		D)	$100


2.	A builder figures $25 for waste allowances as part of a $250 material cost. What is the percent of waste allowance?
		A)	25
		B)	25%
		C)	10
		D)	10%


3.	In preparing a bid, a carpenter figures that $22 per hundred will go to overhead expenses. What is the percent of overhead?
		A)	22/100
		B)	100/22
		C)	22%
		D)	4.55%


4.	A supplier provides a discount of $5 for the first $50 and $10 for the next $50 spent. What is the discount percent for spending $100?
		A)	5
		B)	5%
		C)	10%
		D)	15%


5.	A carpenter receives a lumber shipment in which 18 pieces per hundred are imperfect. What is the waste allowance for this shipment?
		A)	100/18
		B)	18/100%
		C)	18%
		D)	18