Wood Technology & Processes

Adding Fractions

Fractions can be added quickly once you have found a common denominator. The common denominator is the number into which the denominators of all the fractions can be divided. For example, to add 3/4 plus 1/2, you need to find a common number for the denominators 4 and 2. You can find the common denominator by multiplying each denominator by 1, 2, 3, 4, etc., until you find a common number.

Practice Exercise

Add the fractions 1/2 and 3/4.

Hint: Another way to find the common denominator is to multiply the denominators. For example, if you multiply 4 × 2, the result, 8, is a common denominator. Both 2 and 4 can be divided into 8. However, this method will not always yield the lowest common denominator, and you may find yourself working with some large numbers.

1.		Add the fractions 1/4 and 3/8.
			A)	3/4
			B)	4/8
			C)	5/4
			D)	5/8
2.		Add the fractions 1/2 and 5/16.
			A)	13/16
			B)	6/16
			C)	5/16
			D)	5/32

Practice Exercise

Add the mixed numbers 3 3/8 and 6 1/2.

3.		A carpenter worked 7 1/2 hours on Wednesday, 6 1/4 hours on Thursday, and 4 3/4 hours on Friday to finish a house addition. How many hours did the carpenter work?
			A)	18
			B)	18 1/2
			C)	18 3/4
			D)	18 5/8
4.		A closet will have two interior shelves. Each shelf will be 19 3/4" long. Allowing 1/8" for one saw kerf, what length of shelving will need to be ordered?
			A)	19 4/32''
			B)	19 7/8''
			C)	39 4/32''
			D)	39 5/8''
5.		You have two pieces of quarter-round molding left to cut and install. One piece is 60 1/2" and the other is 11 3/4''. Allowing 1/8'' for one saw kerf, what is the length of the molding you need?
			A)	72 1/4''
			B)	72 2/8''
			C)	72 3/8"
			D)	72 4/4''