133.How Long Would C Take
★★★puzzlesSIG
A finishes a job in 100 minutes and B finishes the same job in 120 minutes. They work together for 40 minutes, then C joins and the three of them complete the remaining work in a further 10 minutes. How long would C take to do the whole job alone?
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Add rates, not times. Work out the fraction completed in the first 40 minutes, then solve for C's rate over the final stretch.
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