# Carpentry & Building Construction

## Math Activities :

### 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, & Abbreviationspercent - 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