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[例题]一项工作单独由一个人去做完,甲要8小时,乙要12小时,甲先单独做5小时后,剩下的由乙单独做完,还要多少小时完成?一、假设法。假设这项工作任务是生产960个机器零件,那么甲每小时就生产(960/8)个零件,乙每小时生产(960/12)个零件,甲先生产5小时后,还剩(960-960/8×5)个零件,乙完成剩下的零件就需要(960-960/8×5)/(960/12)=4.5(小时)。二、工程法。把这项工作总量看作“1”.甲每小时完成的工作量是1/8,乙每小时完成的工作量是1/12。甲先做5小时完成的工作量是1/8×5=5/8。剩下的工作量是1-5/8=3/8。那么乙单独完成剩下的工作量的时间是(3/8)/(1/12)=4(1/12)(小时),综合算式是:(1-1/8×5)/(1/12)=4(1/2)(小时)。
[Example] A work done by a person alone, A to 8 hours, B to 12 hours, A first alone to do 5 hours later, the rest of the B done alone, but also how many hours to complete? law. Assuming that this task is to produce 960 machine parts, then A produces 960/8 parts per hour, B produces 960/12 parts per hour, and after 5 hours of first production, 960- 960/8 × 5) parts, B to complete the remaining parts will need (960-960 / 8 × 5) / (960/12) = 4.5 (hours). Second, the engineering method. Think of the total number of jobs as “1.” The number of jobs done per hour is 1/8, and the number of jobs per hour B is 1/12. A first five hours to complete the workload is 1/8 × 5 = 5/8. The remaining workload is 1-5 / 8 = 3/8. Then B alone (3/8) / (1/12) = 4 (1/12) (hour), the comprehensive formula is: (1-1 / 8 × 5) / (1 / 12) = 4 (1/2) (hours).