Question : A takes 2 hours 30 minutes more than B to walk 40 km. If A doubles his speed, then he can make it in 1 hour less than B. What is the average time taken by A and B to walk a 40 km distance?

Question : Two pipes A and B can fill a tank in 12 hours and 18 hours, respectively. Both pipes are opened simultaneously. In how much time will the empty tank be filled completely?

Question : Pipes A and B can fill a tank in 18 minutes and $22 \frac{1}{2}$ minutes, respectively while pipe C can empty the full tank in 12 minutes. A and B are opened together for 6 minutes and then closed. Now C is opened. C alone will empty the tank in ____.

Question : X can do a work in 3 days, Y can do three times the same work in 8 days, and Z can do five times the same work in 12 days. If they have to work together for 6 hours a day, then how much time will they take to complete the work?

Question : The ratio of the fifth and sixth terms of the sequence 1, 3, 6, 10, ..... is: