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7-8 Work Problems Objective: To solve work problems 7-8 Work Problems Use the formula: Work Rate X time = work done rt=w Work rate means the fractional part of a job done in a given unit of time. 7-8 Work Problems Example 1: Sheri can rake the lawn in 2 h. Her work rate is the part of the job she can do in 1 h. r t = w r = w/t r = 1/2 Therefore her work is ½ job per hour. 7-8 Work Problems Example 2: Josh can split a cord of wood in 4 days. His father can split a cord in 2 days. How long will it take to split a cord of wood if they work together. 7-8 Work Problems Example 2: Josh can split a cord of wood in 4 days. His father can split a cord in 2 days. How long will it take to split a cord of wood if they work together. Step 1: Find the number of days the job will take them. Step 2: Let x = number of days needed Step 3: Since josh does the job in 4 days: his work rate = ¼. 7-8 Work Problems Example 2: Josh can split a cord of wood in 4 days. His father can split a cord in 2 days. How long will it take to split a cord of wood if they work together. Step 3: Since his father does the job in 2 days his work rate =1/2. Work rate X Time Josh Father 1/4 1/2 X x = Work done 7-8 Work Problems Example 2: Work rate X Time Josh Father 1/4 1/2 = Work done X x Step 3: Josh’s part + Father’s Job is whole job. Step 4: Solve 7-8 Work Problems Example 3: Robot A takes 6 min to weld a fender. Robot B takes only 5 ½ min. If they work together for 2 min. How long will it take Robot B to finish welding the fender by itself. X = number of minutes needed for Robot B to finish. Robot B’s work rate = 1 5 1/2 Work rate X Time Robot A Robot B 1/6 2/11 2 2+x = Work done 7-8 Work Problems Example 3: Work rate X Time Robot A Robot B 1/6 2/11 = Work done 2 2+x A’s part of job + B’s part = whole job 7-8 Work Problems Homework: P. 328 1 – 15 odds