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tia_tia [17]
2 years ago
10

Grace and her brother Sid want to raise money to go to band camp. Their parents have agreed to help them up to $400 by paying th

em $25 when one of them mows the lawn and $10 for each hour that one of them babysits their younger brother. They will have to do a combination of both chores in order to earn the money.
Select the equation that represents the number of lawns they can mow, m, and hours they can babysit, b, to earn $400.
Mathematics
1 answer:
Cerrena [4.2K]2 years ago
6 0

Answer:

I think it would be 25m + 10b = 400

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A tank with a capacity of 1000 L is full of a mixture of water and chlorine with a concentration of 0.02 g of chlorine per liter
faltersainse [42]

At the start, the tank contains

(0.02 g/L) * (1000 L) = 20 g

of chlorine. Let <em>c</em> (<em>t</em> ) denote the amount of chlorine (in grams) in the tank at time <em>t </em>.

Pure water is pumped into the tank, so no chlorine is flowing into it, but is flowing out at a rate of

(<em>c</em> (<em>t</em> )/(1000 + (10 - 25)<em>t</em> ) g/L) * (25 L/s) = 5<em>c</em> (<em>t</em> ) /(200 - 3<em>t</em> ) g/s

In case it's unclear why this is the case:

The amount of liquid in the tank at the start is 1000 L. If water is pumped in at a rate of 10 L/s, then after <em>t</em> s there will be (1000 + 10<em>t</em> ) L of liquid in the tank. But we're also removing 25 L from the tank per second, so there is a net "gain" of 10 - 25 = -15 L of liquid each second. So the volume of liquid in the tank at time <em>t</em> is (1000 - 15<em>t </em>) L. Then the concentration of chlorine per unit volume is <em>c</em> (<em>t</em> ) divided by this volume.

So the amount of chlorine in the tank changes according to

\dfrac{\mathrm dc(t)}{\mathrm dt}=-\dfrac{5c(t)}{200-3t}

which is a linear equation. Move the non-derivative term to the left, then multiply both sides by the integrating factor 1/(200 - 5<em>t</em> )^(5/3), then integrate both sides to solve for <em>c</em> (<em>t</em> ):

\dfrac{\mathrm dc(t)}{\mathrm dt}+\dfrac{5c(t)}{200-3t}=0

\dfrac1{(200-3t)^{5/3}}\dfrac{\mathrm dc(t)}{\mathrm dt}+\dfrac{5c(t)}{(200-3t)^{8/3}}=0

\dfrac{\mathrm d}{\mathrm dt}\left[\dfrac{c(t)}{(200-3t)^{5/3}}\right]=0

\dfrac{c(t)}{(200-3t)^{5/3}}=C

c(t)=C(200-3t)^{5/3}

There are 20 g of chlorine at the start, so <em>c</em> (0) = 20. Use this to solve for <em>C</em> :

20=C(200)^{5/3}\implies C=\dfrac1{200\cdot5^{1/3}}

\implies\boxed{c(t)=\dfrac1{200}\sqrt[3]{\dfrac{(200-3t)^5}5}}

7 0
3 years ago
Mr. and Mrs. Simpson went to the movies. They bought some popcorn for $25.50, two boxes of candy for $18 and two drinks for $14.
Ne4ueva [31]
You add all of those numbers together and get your answer which is 60, so basically like this

25.50 + 14.25 + 18 + 2.25 = 60
4 0
3 years ago
Will the shape shrink or enlarge?
aleksklad [387]
The shape will shrink
8 0
3 years ago
I need help with this question please
ludmilkaskok [199]

Answer:

  62

Step-by-step explanation:

The enclosing rectangle is 24 units long and 12 units high. Its area is ...

  (24 units)(12 units) = 288 square units

The white circles obviously cover more than half the area, so the only viable answer choice is 62.

__

If you want to go to the trouble to actually figure it out, you can find the area of each circle using the area formula ...

  A = πr² = (3.14)(6²) = 113.04

Then both circles have an area of 2×113.04 = 226.08, and the shaded area is the difference between that and the rectangle area:

  shaded area = 288 -226.08 = 61.92 ≈ 62

5 0
3 years ago
A survey was conducted to determine the popularity of three foods among students. The data collected from 75 students are summar
Andrews [41]

Answer:

20

Step-by-step explanation:

Total no = 75

N (P) = 48 , N (H) = 45 , N (T) = 58

N (P∩H) = 28 , N (H∩T) = 37 , N (P∩T) = 40

N (P∩H∩T) = 25

Total no = N (P) + N (H) + N (T) - N (P∩H)  -  N (H∩T) - N (P∩T) + N (P∩H∩T) + neither

75 = 48 + 45 + 58 - 28 - 37 - 40 + 25 + neither

75 = 71 + neither → neither = 4

N (only P) = N (P) - N (P∩H)  - N (P∩T)  + N (P∩H∩T) = 48 - 28 - 40 + 25 = 5

N (only H) = N (H) - N (P∩H) - N (H∩T) +  N (P∩H∩T) = 45 - 28 - 37 + 25 = 5

N (only T) = N (T) - N (H∩T) - N (P∩T) + N (P∩H∩T) = 58 - 37 - 40 + 25 = 6

So, total liking either one or neither = 4 + 5 + 5 + 6 = 20

4 0
3 years ago
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