Aptitude - Pipes and Cistern - Discussion

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.

I have solved it my way. First take the lcm of 12, 15 and 20 which is 60. So we assume the total capacity of tank to b 60 units.

That means A fills 5, B fills 4 and C fills 3 in 1 hr.
For the first hr A and B are opened so tank filled is 9 (5+4).
For the second hr A and C are opened so tank filled in 2nd hr is 8 (5+3).
So total tank filled in 2 hrs is 9+8=17. So in 6hrs 51 unit of tank is filled.

Now only 9 units of tank is to be filled which will b filled in next hr which is 7th hr and in this hr B will b opened. So in 7th hr 5 (By A) +4 (By B) =9unit will be filled which is sufficient to fill the remaining tank.

Hene total tank will be filled in 7 hrs. Hope you all got this.

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

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

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.

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

I can't understand plssssss explain it.

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

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

1st operation is repeated here and atlast we have to check the left period check it.