When we add or subtract fractions, we come across two different scenarios. The first is when the denominators are the same. The second occurs when the denominators are different. When the denominators are different we must obtain a common denominator before we can add or subtract.

Test Objectives
• Demonstrate the ability to add/subtract fractions with a common denominator
• Demonstrate the ability to find the LCD (Least Common Denominator)
• Demonstrate the ability to add/subtract fractions without a common denominator

#1:

Instructions: Find the LCD of the fractions.

a) $$\frac{1}{8}, \frac{1}{12}$$

b) $$\frac{2}{3}, \frac{5}{18}$$

c) $$\frac{2}{14}, \frac{3}{50}, \frac{5}{64}$$

#2:

Instructions: Perform each indicated operation.

a) $$\frac{4}{25}+ \frac{6}{25}$$

b) $$\frac{8}{11}+ \left(-\frac{4}{11}\right)$$

c) $$\frac{6}{7}- \frac{5}{7}$$

d) $$\frac{7}{12}- \frac{4}{12}$$

#3:

Instructions: Perform each indicated operation.

a) $$\frac{3}{7}+ \frac{1}{7}+ \frac{2}{7}$$

b) $$\frac{9}{2}- \frac{3}{2}- \frac{11}{2}$$

c) $$\frac{4}{5}+ \frac{3}{5}- \frac{8}{5}- \frac{7}{5}$$

#4:

Instructions: Perform each indicated operation.

a) $$\frac{2}{18}+ \frac{5}{20}$$

b) $$\frac{3}{38}- \frac{2}{133}$$

#5:

Instructions: Perform each indicated operation.

a) $$\frac{5}{12}+ \frac{4}{21}+ \left(-\frac{6}{24}\right)$$

Written Solutions:

#1:

Solutions:

a) $$24$$

b) $$18$$

c) $$11{,}200$$

#2:

Solutions:

a) $$\frac{2}{5}$$

b) $$\frac{4}{11}$$

c) $$\frac{1}{7}$$

d) $$\frac{1}{4}$$

#3:

Solutions:

a) $$\frac{6}{7}$$

b) $$-\frac{5}{2}$$

c) $$-\frac{8}{5}$$

#4:

Solutions:

a) $$\frac{13}{36}$$

b) $$\frac{17}{266}$$

#5:

Solutions:

a) $$\frac{5}{14}$$