A sum of money amounts to 5,200 in 5 years and to 5,680 in 7 years at simple interest. The rate of interest per annum is-

A milk in vendor has 21 liters of cow milk, 42 liters of toned milk and 63 liters of double toned milk. If he wanted to pack them in cans so that each can contains same liters of milk and does not want to mix any two kinds of milk in a can, then the least number of cans required is : 

Pipes P and Q can fill a tank in 18 and 27 minutes, respectively, whereas Pipe R can empty the full tank in 54 minutes.  P and Q were opened together for 6 minutes and then   closed and R was opened. The tank was emptied by R alone in :

The ratio of ages of A and B 4 years ago was 5 : 3. The sum of present ages of A, B and C is 80 years. If present age of C is equal to sum of present ages of A and B. find the present age of A.

If $${144\over0.144}={14.4\over x}$$, then the value of x is

A boat covers 35 km downstream in 2 h and covers the same distance upstream in 7 h. Find the speed (in km/h) of the boat in still water.  

The average age of Ram and his son is 48 years. The ratio of their ages 13 years ago was 11 : 3. What is the present age of son?