Carpentry & Building Construction © 2004

Math Activities :

Self-Check Math Activity 11

Converting Percents to Decimals

Carpenters convert percents to decimals when figuring costs and waste allowances. To convert a percent to a decimal, move the decimal point two places to the left. If using a calculator, input the percent and then divide by 100. Round to the nearest 10,000^th, which is 4 decimal places. Finally, drop the percent symbol.

Terms, Symbols, & Abbreviations
10,000^th - 1/10,000, or 0.0001. Carpenters round decimals to the nearest 10,000^th, or 4 decimal places, because they measure to the nearest 1/16 inch. In decimals, 1/16 inch equals 0.0625 (625/10,000).

Practice Exercise

Convert 178% to a decimal.
Step 1	Move the decimal point two places to the left
	The number 178 becomes 1.78
	OR, use a calculator:
	Divide the amount by 100.
	178 ÷ 100 = 1.78
Step 2	Be sure to drop the percent symbol from the result.

Problem Exercises


1.	Convert 152.8% to a decimal.
		A)	15,280
		B)	15.28
		C)	1.528
		D)	0.1528


2.	Convert 6.2% to a decimal.
		A)	0.062%
		B)	6.20
		C)	0.620
		D)	0.062


3.	Convert 72% to a decimal.
		A)	0.72
		B)	7.20
		C)	72.0
		D)	7,200


4.	The sales tax on a supply receipt is 4.5%. What is the decimal for the sales tax?
		A)	4.5
		B)	0.45
		C)	0.045
		D)	45.00


5.	To check the builder's calculations for a 13% waste allowance, what decimal will you use?
		A)	13.0
		B)	0.13
		C)	0.013
		D)	0.001