It takes 6 minutes and 12 minutes, respectively, to run two computer programs when they are run one at a time. However, their speeds are reduced by 50% and 40%, respectively, if running in parallel. If a PC starts running the two programs together, how long will it take for them to finish?
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Correct Answer: D. 16.8 minutes
At a 50% reduced speed, the first program will take (6×100)/(100-50)=12 minutes to complete, and at a 40% reduced speed, the second program will take (12×100)/(100-40)=20 minutes to complete. However, if they are started together, the first program will be completed after the first 12 minutes, and the second program will run alone at the regular speed. In 12 minutes, only (12×100)/20=60% of the second program will be complete. For the remaining 40%, it will run at its full speed and take another (12×40)/100=4.8 minutes to complete. The total time required to finish both the programs is 12+4.8=16.8 minutes.
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