A swimming pool can be filled by pipe A in 3 hours and by pipe B in 6 hours, each pump working on its own. At 9 am pump A is started. At what time will the swimming pool be filled if pump B is started at 10 am? Choose the correct choice from the following answers
A) 11:20
B) 11:30
C) 11:40
D) 11:50
E) 11:60
the rates of the two pumps are   pump A: 1 / 3 , pump B: 1 / 6   Working together, If pump A works for t hours then pump B works t - 1 hours since it started 1 hour late. Hence   t * (1 / 3) + (t - 1) * (1 / 6) = 1   Solve for t   t = 7 / 3 hours = 2.3 hours = 2 hours 20 minutes.   The swimming pool will be filled at   9 + 2:20 = 11:20   11:20nswer 11:20
<result>A</result>
A swimming pool can be filled by pipe A in 3 hours and by pipe B in 6 hours, each pump working on its own. At 9 am pump A is started. At what time will the swimming pool be filled if pump B is started at 10 am?