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: a copy machine , working at a constant rate , makes 40 copies per minute . a second copy machine , working at a constant rate , makes 55 copies per minute . working together at their respective rates , how many copies do the two machines make in half an hour ? 
Options: a ) 90 , b ) 2,700 , c ) 4,500 , d ) 5,400 , e ) 2,850
[EX A]: e

[EX Q]: Problem: a can finish a work in 20 days , b in 15 days and c in 12 days . b and c start the work but are forced to leave after 2 days . the remaining work was done by a in : 
Options: a ) 10 , b ) 11 , c ) 12 , d ) 13 , e ) 14
[EX A]: e

[EX Q]: Problem: two numbers have a h . c . f of 20 and a product of two numbers is 2560 . find the l . c . m of the two numbers ? 
Options: a ) 140 , b ) 150 , c ) 160 , d ) 128 , e ) 180
[EX A]:
d