Two pipes A and B can fill a tank in 10 and 20 minutes respectively.If both pipes are opened simultaneously,after how many minutes should pipe B be closed so that the tank is full in 8 minutes?
A. 3 min
B. 4 min
C. 2 min
D.5 min
The difference between a two-digit number and the number obtained by interchanging the digits is 36. What is the difference between the sum and the difference of the digits of the number if the ratio between the digits of the number is 1 : 2 ?