P and Q together can do a job in 7 days. P is twice as efficient as Q. In how many days can P alone do the job?
P and Q can do the work in 7 days
efficiancy of P : efficency of Q = 2 : 1
total work = 7 * 3 = 21Â
P can alone do the work in $$\frac{21}{2}$$ = 10.5 days
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