Question 1183385: Hello
A pipe can empty a tank in 40 minutes.
A second pipe with diameter twice as much as
that of the first is also attached with the tank to empty it.
The two pipes together can empty the tank in 8
minutes.
I don't understand how they got 8?
How would I go about solving this?
Thanks in advance,
Found 5 solutions by math_helper, MathTherapy, greenestamps, ikleyn, Edwin McCravy:
Answer by math_helper(2461)   (Show Source):
Answer by MathTherapy(10552)  (Show Source):
You can put this solution on YOUR website!
Hello
A pipe can empty a tank in 40 minutes.
A second pipe with diameter twice as much as
that of the first is also attached with the tank to empty it.
The two pipes together can empty the tank in 8
minutes.
I don't understand how they got 8?
How would I go about solving this?
Thanks in advance,
8 minutes is GIVEN as part of the problem. You DON'T have a question that needs to be answered.
Is the time needed for the 2nd pipe to empty the tank, by itself, needed?
That's a question that's usually asked.
Answer by greenestamps(13200)  (Show Source):
You can put this solution on YOUR website!
The rate at which water flows through the pipes is proportional to the cross sectional area of the pipes. Since the diameter of the second pipe is 2 times the diameter of the first, water flows through the second pipe at a rate 2^2=4 times as fast as through the first pipe.
So having both pipes working is like having 1+4=5 of the first pipes. Then, since the first pipe can empty the tank in 40 minutes, the two pipes together can empty it in 40/5 = 8 minutes.
-----------------------------------------------------------
Note that a couple of tutors who responded to this post failed to understand what the reader was asking for.
He KNOWS the answer is 8 minutes; what he is clearly asking for is help to understand HOW to get that answer.
My response above and the one from tutor @Math_helper both do that, in different ways....
Answer by ikleyn(52787)  (Show Source):
You can put this solution on YOUR website! .
I do not think that in this problem they assume that you are familiar with the basics of hydraulics
to make a conclusion that the flow rate through the pipe of the doubled diameter is 4 times
the flow rate through the narrow pipe.
Simply, you did not read the problem to the end and posted the problem in the incomplete mode.
I am 179% sure that the next phrase in the problem, which you missed to read and to print, is
How fast the second pipe can empty the tank, if it works alone ?
The info about flow rate is not intended for you to find out "why ?"
It is simply the "given part", after which the question follows.
On solving such problems, look the lessons
- Using Fractions to solve word problems on joint work
- Solving more complicated word problems on joint work
- Selected joint-work word problems from the archive
Read them and get be trained in solving joint-work problems.
//////////////
Next time, when you post your problems/questions to this forum,
print and post them IN FULL, word-in-word, from the very beginning to the very end,
INCLUDING the QUESTION itself and the question sign after it . . .
These are the RULES of this forum,
and you just violated them in your post.
About the rules of the forum, see this Internet page
https://www.algebra.com/tutors/students/ask.mpl?action=ask_question&topic=Equations&return_url=http://www.algebra.com/algebra/homework/equations/
from which you post your problems.
It is assumed that you read these rules before posting.
It is also assumed that you do understand what is written in that page and follow the rules.
Those who violate them, work against their own interests.
/\/\/\/\/\/\/\/
After observing all arrived answers, I become even more certain, than I was certain before,
that the only right strategy to treat such posts is to delete them.
Answer by Edwin McCravy(20056)  (Show Source):
|
|
|
