In this task, you need to answer the given multiple-choice question on the physics. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

[EX Q]: Problem: 13 buckets of water fill a tank when the capacity of each bucket is 51 litres . how many buckets will be needed to fill the same tank , if the capacity of each bucket is 17 litres ? 
Options: a ) 39 , b ) 28 , c ) 23 , d ) 12 , e ) 24
[EX A]: a

[EX Q]: Problem: on a trip covering 400 km , a bicyclist travels the first 100 km at 20 km per hour and the remainder of the distance at 15 km per hour . what is the average speed , in km per hour , for the entire trip ? 
Options: a ) 15.5 , b ) 16.0 , c ) 16.5 , d ) 17.0 , e ) 17.5
[EX A]: b

[EX Q]: Problem: hcf and lcm two numbers are 20 and 396 respectively . if one of the numbers is 36 , then the other number is ? 
Options: a ) 36 , b ) 66 , c ) 132 , d ) 264 , e ) 220
[EX A]:
e