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sveta [45]
3 years ago
11

An inlet pipe can fill a water tank in 12 hours. An outlet pipe can drain

Mathematics
1 answer:
Ira Lisetskai [31]3 years ago
6 0
<h3>Answer:   30 hours</h3>

============================================================

Explanation:

Let's consider the tank's full capacity is 240 gallons. I'm picking this number because 12*20 = 240.

If the tank is 240 gallons, then the inlet pipe can fill it at a rate of 240/12 = 20 gallons per hour. Note after 12 hours, we have 12*20 = 240 gallons filled assuming the outlet pipe is sealed shut.

At the same time, the outlet pipe is draining at a rate of 240/20 = 12 gallons per hour. After 20 hours, the outlet pipe would drain out 12*20 = 240 gallons assuming the inlet pipe is not adding any water.

With the two pipes playing this tug-of-war battle, the inlet pipe ultimately wins because it's adding more gallons of water each hour, compared to the amount drained per hour. The net change is +20-12 = 8 gallons per hour.

This means it will take 240/8 = 30 hours to fill the tank with both pipes open.

----------------------------------

Another approach:

The inlet pipe can fill the tank in 12 hours, so it gets 1/12 of the job done per hour. The outlet pipe drains the tank in 20 hours, so it gets 1/20 of the job done in one hour.

The net change is 1/12 - 1/20 = 5/60 - 3/60 = 2/60 = 1/30

This means that when both pipes are open, 1/30 of the job is done per hour. By "job", I mean "filling the tank".

If x is the number of hours needed to do one full job, then we can multiply that by the unit rate (1/30) and set the result equal to 1

(rate)*(time) = 1 job

(1/30)*x = 1

x = 30*1

x = 30

It takes 30 hours to do the job with both pipes open.

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Person A takes 2.3 days to paint the house working alone

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<em><u>Solution:</u></em>

Let "x" be the number of days it takes person A  to paint the house

Person A can paint the neighbor's house 6 times as fast as Person B

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Number of days it takes person B to paint the house = 6x

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3 0
3 years ago
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k:\ y=m_1x+b_1\\\\l:\ y=m_2x+b_2\\\\k\ ||\ l\iff m_1=m_2\\\\k\ \perp\ l\iff m_1m_2=-1

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k:\ 9x+7y=6\ \ \ |-9x\\\\7y=-9x+6\ \ \ \ |:7\\\\y=-\dfrac{9}{7}x+\dfrac{6}{9}\to m_1=-\dfrac{9}{7}\\\\l:\ y=m_2x+b\\\\l\ \perp\ k\iff-\dfrac{9}{7}m_2=-1\ \ \ \ |\cdot\left(-\dfrac{7}{9}\right)\\\\m_2=\dfrac{7}{9}\to\ l:\ y=\dfrac{7}{9}x+b

We know. The line <em>l</em> passes throught the point (9, -7). Substitute the coordinates of the poin to the equation of line<em> l </em>:

-7=\dfrac{7}{9}\cdot9+b\\\\-7=7+b\ \ \ \ |-7\\\\b=-14

y=\dfrac{7}{9}x-14\ \ \ \ |\cdot9\\\\9y=7x-126\ \ \ \ |-9y\ |+126\\\\7x-9y=126

Answer: y=\dfrac{7}{9}x-14\to7x-9y=126


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