Question

Please explain this question and Help me understand the chapter in a few points

Answer 1

find efficiency by dividing hours by 1

i.e 1/4 and 1/6

together they will take 1/4 + 1/6 = 10/24

now take its reciprocal it thus ans=12/5

Answer 2

my friend , before getting  into the question you must understand curtain points

step1
if a cistern that x hour in a day then,
for one hour =1/x
in this case ,it is 1/4 and 1/6 

step 2
 ,if the ask for filling together then u must add them ,
1/x1+1//x2
in the case it is 1/4+1/6
=6+4/24=10/24  

step 3, you must reciprocal it to get the total hours
in this case we get,
24/10=12/5 

therefore c is the correct answer