A fills spirit tanker in 8 hours and B fills in 12 hours. They are opened alternately for one hour each, starting with A at 10. When will the tank be filled?

(a) 5.30PM
(b) 6.00PM
(c) 7.30PM
(d) 10.00PM

• (c) 7:30 PM
  
  In 2 hours, (1/8)+(1/12)=5/24 tank is filled
  So in 4*2=8 hours, 4*5/24=5/6 tank is filled
  In 9th hour again A will fill, so total (5/6)+(1/8)=23/24 tank is filled and
  In next hour remaining 1/24 will be filled by B, in (1/24)/(1/12)=1/2 hour
  So total time taken, 9+1/2 hours.
  Hence tank is filled at 10 AM+9 1/2 hours=7:30 PM
• 8 years agoHelpfull: Yes(2) No(1)