184 Chapter 3 Fractions and Mixed Numbers: Addition and Subtraction Answers 8. in. 9. a. gal was used. 13 16 b. 13 gal was left over. 48 7 15 3. Applications Involving Unlike Fractions Applying Operations on Unlike Fractions A new Kelly Safari SUV tire has -in. tread. After being driven 50,000 mi, the tread depth has worn down to in. By how much has the tread depth worn away? Solution: In this case, we are looking for the difference in the tread depth. The LCD is 32. Multiply numerator and denominator by 2 because The fractions are now like. Subtract. The tire lost 7 in. in tread depth after 50,000 mi of driving. 32 7 32 14 32 7 32 16 2 32. 7 2 16 2 7 32 7 16 7 32 Difference in tread depth a original tread depth b a final tread depth b 7 32 7 16 Example 7 Tread TIP: You can check your result by adding the final tread depth to the difference in tread depth to get the original tread depth. 7 32 7 32 14 32 7 16 Skill Practice 8. On Monday, in. of rain fell on a certain town. On Tuesday, in. of rain fell. How much more rain fell on Monday than on Tuesday? 15 2 3 Applying Operations on Unlike Fractions Example 8 An oil tank contains 2 liters (L) of oil. A slow leak has occurred, and oil leaks out at a rate of L per day. After 7 days, a mechanic fixed the leak and poured in L of oil back into the tank. How much oil is now in the tank? Solution: To find the current amount in the tank, we must determine the amount lost and the amount added. The amount lost is given by the amount lost per day times 7 days. 16 a 1 16 The amount lost in 7 days is 7 L. b 172 1 16 7 1 7 16 38 1 16 Skill Practice 9. Maggie mixed gal of “winter wheat’’ paint with gal of “forest green.” Then she used of the mixture to paint a wall. a. How much paint did she use? b. How much paint is left over? 34 1 3 3 4
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