Tham khảo tài liệu 'new sat math workbook episode 2 part 2', ngoại ngữ, ngữ pháp tiếng anh phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Problem Solving in Algebra 185 8. WORK PROBLEMS In most work problems a job is broken up into several parts each representing a fractional portion of the entire job. For each part represented the numerator should represent the time actually spent working while the denominator should represent the total time needed to do the job alone. The sum of all the individual fractions must be 1 if the job is completed. Example John can complete a paper route in 20 minutes. Steve can complete the same route in 30 minutes. How long will it take them to complete the route if they work together Solution John Steve Time actually spent Time needed to do x x TT 1 entire job alone 20 30 Multiply by 60 to clear fractions. 3x 2 x 60 5x 60 x 12 Example Mr. Powell can mow his lawn twice as fast as his son Mike. Together they do the job in 20 minutes. How many minutes would it take Mr. Powell to do the job alone Solution If it takes Mr. Powell x hours to mow the lawn Mike will take twice as long or 2x hours to mow the lawn. Mr. Powell Mike 20 20 x 2x Multiply by 2x to clear fractions. 40 20 2x 60 2x x 30 minutes 186 Chapter 12 Exercise 8 Work out each problem. Circle the letter that appears before your answer. 1. Mr. White can paint his barn in 5 days. What part of the barn is still unpainted after he has worked for X days A x B 5 X C x75 X D 5-X X E 5 2. Mary can clean the house in 6 hours. Her younger sister Ruth can do the same job in 9 hours. In how many hours can they do the job if they work together A 3 2 3 B 3 3 C 4 D 41 E 4 3. A swimming pool can be filled by an inlet pipe in 3 hours. It can be drained by a drainpipe in 6 hours. By mistake both pipes are opened at the same time. If the pool is empty in how many hours will it be filled A 4 B 4 2 C 5 D 52 E 6 4. Mr. Jones can plow his field with his tractor in 4 hours. If he uses his manual plow it takes three times as long to plow the same field. After working with the tractor for two hours he ran out of gas and .
