ddippset:
Wait. Answer is 6.667 minutes. Wait for explanation. Let the capacity of the tank be X. Then the Pipes have flow rates of x/30, x/20 and x/15 per minute respectively. So the total flow rate all working together would be x/30+x/20+x/15=3x/20 lets say litres per minute. Now the time for the 3 would be capacity divided by flow rate = X divided by 3x/20= 20/3=6.667 minutes. CLAP FOR ME!

you are correct but i used probablity approach as i am not a mathematician but a statistician

hahn:




I know I got it right.

Answer my own question then if you're such a whiz. Many people came from the north, many from the south, many from the east and many from the west and they all assembled in the middle.

How many people are there?

4

PassingShot:
Your question is meant to read "how many minutes will be required to fill the tank if all pipes were switched on at the same time?"

The answer is 6.66 minutes. I will explain it:

Let the tank size x be assumed to be 100 liters.

If Pipe A can fill it in 20 minutes, pipe A pumps 5 liters per minute (100/20)
If Pipe B can fill it in 30 minutes, it then pumps 3.33 liters per minute (100/30min)
If Pipe C can fill it in 15 mins, then it pumps 6.6 liters per minute (100/15)

When all pipes are switched on together, they jointly pump about 15 liters per minute (5+3.33+6.6 liters).

Therefore, to fill 100 liter tank, 6.6666 approx. 6.76 minutes will be needed (100/15 liter per minute).

NB: Irrespective of the figure used for the tank capacity, the same result/answer will be achieved. The reason being that you will eventually divide the tank capacity assumed (30, 50, 100 or whatever figure) by what can be jointly pumped by the pipes in one minute (which varies according to capacity assumed).

Where is my prize OP?

Let me be clearer here. using the calculated flow rate above. flow rates: A=5l/m, B=3.33l/m, C=6.6l/m

for first minute only A contributes: 5liter; in the second mins, A & B contributes 5litres and 3.33liters respectively totaling 8.33liters
total liters contributed in the 1st and 2and minutes=13.33liters____ this implies that for the first two minutes 13.33liters of the tank is filled
remaining volume of tank to be fill=100-13.33= 86.67liters
3rd minute and above A, B & C contribute with a total flow rate of 15liters/min to fill 86.67liters and this will take 86.67/15=5.778min
hence the total time required=5.778+2=7.78mins

ddippset:
Wait. Answer is 6.667 minutes. Wait for explanation. Let the capacity of the tank be X. Then the Pipes have flow rates of x/30, x/20 and x/15 per minute respectively. So the total flow rate all working together would be x/30+x/20+x/15=3x/20 lets say litres per minute. Now the time for the 3 would be capacity divided by flow rate = X divided by 3x/20= 20/3=6.667 minutes. CLAP FOR ME!

They were not all turned on at the same time but one minute after the other. The op should tell us which pipe was turned on first and which one was turned on last.

PassingShot:

I actually thought the "successive" stmt was an error. Good to find out the result is same whether pipes turned on successively after the other or all turned on at once.
Thanks.

u'r welcome my love

hottestlegs:


you are nearly there if not for the statement 'one successive minutes. the answer is actually: for 2min A & B contributes 13.3mins hence the remaining volums is 1oo-13.3= 86.7; hence it will take A, B & C 86.7/15 =5.78min; therefore total min: 2+5.78= 7.78min

You sabi book

PassingShot:

For exam purpose, we have to simply find out the pump rate per pipe and do just as I did.
Employing your argument which may be valid in real life, then it is save to say there won't be an answer to the question.
Modified*
Got your point now.

Your are correct. I guess the op was considering the source flow rate or pump force and wanted to remove any ambiguity.

Let me flip the question:

A tank of 150litres has 3taps. Each can empty the tank in 30mins, 15mins and 20mins. How long will it take to empty the tank if

a. each tap were opened for 1min successively, and
b. if all the taps were opened at once.

You should know that while you'll have the same answer as the op's for "a"; you will have a different answer for "b".

The total flow rate for "b" wont be the addition of the individual flow rates as will be affected by the shape of the tank and the position of the taps amongst other factors. To calculate it you would need the knowledge of hydraulics and pipe flow engineering.

But yes, you are correct about the ops question.

hottestlegs:



Let me be clearer here. using the calculated flow rate above. flow rates: A=5l/m, B=3.33l/m, C=6.6l/m

for first minute only A contributes: 5liter; in the second mins, A & B contributes 5litres and 3.33liters respectively totaling 8.33liters
total liters contributed in the 1st and 2and minutes=13.33liters____ this implies that for the first two minutes 13.33liters of the tank is filled
remaining volume of tank to be fill=100-13.33= 86.67liters
3rd minute and above A, B & C contribute with a total flow rate of 15liters/min to fill 86.67liters and this will take 86.67/15=5.778min
hence the total time required=5.778+2=7.78mins

You are assuming that "successive" in the ops question means that each pipe will be left open when opening the next pipe. There isn't enough info to make this definitive.

hottestlegs:



Let me be clearer here. using the calculated flow rate above. flow rates: A=5l/m, B=3.33l/m, C=6.6l/m

for first minute only A contributes: 5liter; in the second mins, A & B contributes 5litres and 3.33liters respectively totaling 8.33liters
total liters contributed in the 1st and 2and minutes=13.33liters____ this implies that for the first two minutes 13.33liters of the tank is filled
remaining volume of tank to be fill=100-13.33= 86.67liters
3rd minute and above A, B & C contribute with a total flow rate of 15liters/min to fill 86.67liters and this will take 86.67/15=5.778min
hence the total time required=5.778+2=7.78mins

BRILLIANT.
The prize is yours.
Congrats.

obailala:
Calculating... Wow!... this simple problem almost got me crazy here in the office.


Answer is 7.778 mins

If all pipes are opened at the same time, the tank fills in 6.667 mins, but when 'B' is opened after 1 minute after 'A', and 'C' is opened after 1 minute after 'B', then the tank fills in 7.778 mins

Assuming:
Tank capacity = T

Flowrate of pipe A = T/20
Flowrate of pipe B = T/30
Flowrate of pipe C = T/15

Total time used in filling tank = t (mins)
Pipe A runtime = t
Pipe B runtime = t-1
Pipe C runtime = t-2

Tank capacity = (Total Flowrate) * (Total time)

T = (T/20)t + (T/30)(t-1) + (T/15)(t-2)
T = (Tt/20) + (Tt/30 - T/30) + (Tt/15 - 2T/15)
After some voodoo on the above equation....
70T = 9Tt
70 = 9t
t = 7.778 mins

You smart asses obviously missed where the question said "in one successive minutes"

Perfect solution. I didn't even notice that second part of the question which talked about successive and all that. I score you 10/10.

ALVA001:
Three pipes A, B & C empties into a tank. A can fill it in 20mins, B in 30mins, C in 15. If the three pipes were switched on in one successive minutes, how long does it take them to fill the tank?
Modification.
Plz note, one successive minutes ere actually mean one minute after the oda.A @ 0mins, B 1mins aftr, C 1mins aftr B.
Efforts of all contribitors are well commended.

OK. modification seen. But this still does not state if the opened pipes are left opened when opening the successive one.

cos if they are, then hot legs is correct.

You may need to do another modification.

dialfa:


4

The answer is plenty

my answer is totally different from you guys.
I am getting
3.53 mins

this my calculations!
volume=X m³
time=mins
flow rate=vol÷ time(m³/min)

flow rate for pipes A,B and C is (x/20),(x/30) and (x/15)

at first min,only pipe A is flowing=(x/20)

at second. min,pipe A and B is flowing=(x/20) +(x/30)=a total flow=(x/12)

at third min,pipe A,B and C is flowing =(x/20) + (x/30) + (x/15)= we have a total flow =(3x/20)

aggregate flow at this stage of fill (assume no form of loss)

stage 1 + stage 2 + stage 3

therefore
(x/20)+(x/12)+(3x/20)= total of aggregate flow=(136x/480)

volume= flow rate * time
I.e,
t=480/136=3.53 mins

hottestlegs:


wow! happy that a fellow lady is doing this with me. actually sis the flow rate of the individual pipes are not affected in any way by the 'successive minutes' statement only imply that pipe A is ON for a minute before pipe B and then pipe C. this arrangement can only increase the time it takes to fill the tank than when they are all on simultaneously

Lol. I'm glad you're giving thus a run too. I'm a Mechanical ENGR BTW.

Back to the matter. Stay with me on this...

Pipe 1 that can fill the tank in 30mins was opened for 1min. Then pipe 2 which can fill in 20mins was opened for another 1min; then pipe 3 which can fill for 15mins was opened for another 1 min.

According to your analysis ( which I admit I've not checked thoroughly); each was left opened.

My take:

After the 3rd pipe was opened for 1min, and assuming the tank capacity is 150L; what we have is :

Pipe A flow rate: 5L/min
Pipe B flow rate: 7.5L/min
Pipe C flow rate: 10L/min

After opening the three pipes successively in 3mins, we have : [(5*3)+(7.5*2)+(10*1)]= 40liters piped in after three mins. Which = 13.33L/min.

After this 3rd minute, if all pipes are on until the tank is full ( which kinda negates the whole essence of the purpose if the question) This had made the calculation a little cumbersome but you will have . (5+7.5+10)L/min = 22.5L/min pumping till its filled.

Can you solve that?! Its been made complex!

The truth us that the only we can have thus done simply is to state ( or assume) that each pipe is put off after running it for 1min. And this is why I told passingshot initially that putting all pipes on isn't the same as putting the pipes on successively.

I hope I made some sense. If you still don't get some parts, let's thrash it. Its interesting.

ALVA001 bro, i noticed you were in the race for sahara groups recruitment 2016, i just want ask you how the first interview was and what to expect? Thanks in advance

Thavybe:
ALVA001 bro, i noticed you were in the race for sahara groups recruitment 2016, i just want ask you how the first interview was and what to expect? Thanks in advance

it was pretty easy, we were asked to come along with Nigerian Jersey at Usa 94. And also make A 1 minute video where you are expected to sell your self.
Goodluck.

ddippset:
lol. Forget the English, solve the massssss

The grammatical mathematics must be clear for the mathematical mathematics to be solved..
U are not a good mathematician.

ALVA001:

it was pretty easy, we were asked to come along with Nigerian Jersey at Usa 94. And also make A 1 minute video where you are expected to sell your self.
Goodluck.

Gracias, one more thing please, i don't know if you can remember if the questions were specialty related (e.g accounting questions for acct graduates) or general interview questions. thanks bro

Check these videos out.

Thank me later.



https://www.youtube.com/watch?v=dtzQOGbWPrk&t=16s




https://www.youtube.com/watch?v=is7xfEOOOU4&t=19s

Thavybe:
Gracias, one more thing please, i don't know if you can remember if the questions were specialty related (e.g accounting questions for acct graduates) or general interview questions. thanks bro

No it wasn't. They were general questions.

ALVA001:
No it wasn't. They were general questions.

Alright, thanks man