Two persons A and B working separately can sanitise a building in 6 and 10 hours, respectively. They work in stretches of one hour alternately. If A begins at 8 a.m., then when will the work be finished?

$7\frac{1}{3}$h

A = 6 hours, B = 10 hours

⇒Working on alternate hours, starting with A at 8 am,

1st hour       =    5 units

2nd hour      =    3 units

Every 2 hours  = 8 units

⇒Hence, in 6 hrs, 24 units of work will be completed.

  and in 7 hrs, 29 units of work will be completed.

⇒The remaining work i.e; 1 unit will be completed by B in = \(\frac{1}{3}\)hours.

   Therefore, The Total hours taken to complete work = 7 + \(\frac{1}{3}\) = 

\( { 7}_{3 }^{1 } \) hours.