Aptitude - Pipes and Cistern - Discussion

Why 6hrs are taken, I think question is not clear.

i can not understand this question.
how 3/20 part is filled by A and B in 1 hour?

I can't understand plssssss explain it.

why 2 hours are taken first and then 6...what purpose they are using please explain....

If you take more than 6hrs negative value so tank overflows since no leakage thats why we took upto 6hrs


Why 2 hours are taken first and then 6 is because of easy calculation it is not compulsory take like this since alternative filling


(A + B)'s 1 hour's work= 1/12+1/15=3/20

(A + C)'s hour's work =1/12+1/20=2/15


For 2hrs 17/60

so for 1hr take half from 2hrs i.e 17/60*1/2=17/120

now for 2hrs =17/120+17/120(2*17/120)

for 3hrs=17/120+17/120+120(3*17/120)

for 4hrs=4*17/120

for 5hrs=5*17/120

for 6hrs=6*17/120=17/20 right?

for 7hrs=7*17/120...................


Remaining part=(1-17/20)=3/20
suppose if you take for 7hrs gets negative value total time will be more than time required to fill the tank

Therefore from above part is filled by A and B in 1 hour is 3/20 and the ramaining part also 3/20 that means remaining part takes 1hr

Hence total time = 6hrs + 1hr = 7hrs.

I HAVE TRIED TO SOLVE IT IN MY OWN WAY,PZ REPLY WHETHER ITS IS CORRECT OR NOT

WORK DONE
A IN 1 HOUR = 1\12
B IN 1 HOUR = 1\15
C IN 1 HOUR = 1\20

SINCE A WORKS ALL THE TIME,B AND C WORKS ALTERNATELY
HOURS: 1 2 3 4 5 6 7
PERSONS (A,B) + (A,C) + (A,B) + (A,C)+ (A,B) + (A,C) + (A,B)
VALUE 3/20 2/15 3/20 2/15 3/20 2/ 15 3/20

WATCH CAREFULLY:WHEN U ADD THIS DENOMINATOR COMES TO 60 AND NUMERATOR ALSO TO 60 ie 1 ,SO TANK IS FULL IN 7 HOURS

Hrishi. Your method is trail and error method. How can we say 7 hours directly ?

Is this correct?

A is open all the time Part filled x/12.

B is open for 1 hr = 1/15.
C is open for 1 hr = 1/20.

x/12+ 1/15+ 1/20 = 1.

(5x+4+3)/60 = 1.

x = 60-7)/5 = 53/5 ~~ 5 hrs.

How come you consider 6 hrs duration for the part fillings?

For the first hour, part filled from the tank (1\12)+(1\15) = 3\20.

Second (1\12)+(3\20) = 2\15.

Third (1\12)+(1\15) = 3\20.

Fourth (1\12)+(1\15) = 2\15.

Fifth (1\12)+(1\15) = 3\20.

Lets see how much the tank full in 5 hours.

3*(3\20)+ 2*(2\15) = 43\60 So the tank is not full yet.

For the sixth hour ,part filled from the tank (1\12)+(3\20) = 2\15.

Let's see how much the tank full in 6 hour.

3*(3\20)+3*(1\15) = 17\20 so the tank is not full yet.

For the seventh hour, part filled from the tank(1\12)+(2\15) = 3\20.
Let's see how much the tank full in 7 hour.

4*(3\20)+3*(2\15) = 1 so the tank is completely full after 7 hour.