If time taken finish the work
=x days
∴ Part of work completed in one day
=1∕xCalculation:
P can finish the work in 15 days.
∴ One day work of
P=1∕15And, Q can finish the work in 20 days.
∴ One day work of
Q=1∕20Let P and Q together complete the work in x days.
∴ One day work of P and
Q=1∕20+1∕15=1∕x⇒1∕x=7∕60So, 5 days work of P and Q will be
=5×7∕60=7∕12Now, remaining work=1-7/12=5/12
∴ Number of days required by Q to finish the work
=(5∕12)∕(1∕20)=8 days