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belka [17]
3 years ago
7

Assuming a normal distribution, families spends an average of $500 on their monthly cell phone bills with a standard deviation o

f $75. what is the probability a random families' bill is between $350 and $400?
Mathematics
1 answer:
lara [203]3 years ago
8 0
The probability is 0.69.

We find the z-scores that correspond with each end of the range we're looking for.  To find a z-score, we use the formula:
z=\frac{X-\mu}{\sigma}
\\
\\=\frac{350-500}{75}=\frac{-150}{75}=-2

z=\frac{400-500}{75}=\frac{-100}{75}=-1.33

Using a z-table (http://www.z-table.com) we see that the area under the curve left of the score 350 would be 0.228.  The area under the curve left of the score 400 would be 0.918.  To find just the range between 350 and 400, we subtract the area left of 350 from the area left of 400; this will give us just from 350 to 400:

0.918-0.228 = 0.69.
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Consider the force field and circle defined below.
grin007 [14]

By Green's theorem,

\displaystyle\int_{x^2+y^2=9}\vec F(x,y)\cdot\mathrm d\vec r=\iint_D\left(\frac{\partial(xy)}{\partial x}-\frac{\partial(x^2)}{\partial y}\right)\,\mathrm dx\,\mathrm dy=\iint_Dy\,\mathrm dx\,\mathrm dy

where C is the circle x^2+y^2=9 and D is the interior of C, or the disk x^2+y^2\le1.

Convert to polar coordinates, taking

\begin{cases}x=r\cos\theta\\y=r\sin\theta\end{cases}\implies\mathrm dx\,\mathrm dy=r\,\mathrm dr\,\mathrm d\theta

Then the work done by \vec F on the particle is

\displaystyle\iint_Dy\,\mathrm dx\,\mathrm dy=\int_0^{2\pi}\int_0^3(r\sin\theta)r\,\mathrm dr\,\mathrm d\theta=\left(\int_0^{2\pi}\sin\theta\,\mathrm d\theta\right)\left(\int_0^3r^2\,\mathrm dr\right)=\boxed0

4 0
3 years ago
Lisa wants to use her calculator to square a two-digit positive integer, but she accidentally enters the tens digit incorrectly.
Svetradugi [14.3K]

Answer: Correct two digit number= 24

Step-by-step explanation:

Let

x= tens digit (wrong one)

and y= zeroes digit

and z= tens digit (right one)

Now according to the statement,

(10x+y)² -  (10z+y)² = 2340

Simplifying this we get

(x-z)(5x+y+5z)= 117= 1 * 3 * 3 * 13

So it could either be

x-z=1 or x-z=3

If we take the x-z=1

then 5x+y+5z=117

which is not possible as maximum value we can get from this is 99.

This leaves us with x-z=3

so 5x+y+5z= 39

Put x=3+z

We get,

y+10z= 24

Now as y and z both are single digits so the only possible numbers to fit these are y=4 and z=2.

Put z=2 in x=3+z , we get x=5

So the numbers become 10x+y= 54

and 10z+y= 24

Their sum is 54+24=78

Check

54²-24²= 2340 so it is correct.

7 0
3 years ago
Barb had $112 in her savings account. Then deposited the same amount of money into her savings account in the next 4 months. Now
Kay [80]
• Subtract first: 333 - 112 = 221

• Divide second: 221 ÷ 4(months) = 55.25

• Equation: (333 - 112) ÷ 4

Barb deposited $55.25 each month. 

Hope this helps! :D

~PutarPotato
7 0
3 years ago
Read 2 more answers
Area and percent . ​
siniylev [52]

Answer:

a. 61.92 in²

b. 21.396 ≈ 21.4%

c. $4.71

Step-by-step explanation:

a. Amount of waste = area of rectangular piece of stock - area of two identical circles cut out

Area of rectangular piece of stock = 24 in × 12 in = 288 in²

Area of the two circles = 2(πr²)

Use 3.14 as π

radius = ½*12 = 6

Area of two circles = 2(3.14*6²) = 226.08 in²

Amount of waste = 288 - 226.08 = 61.92 in²

b. % of the original stock wasted = amount of waste ÷ original stock × 100

= 61.92/288 × 100 = 6,162/288 = 21.396 ≈ 21.4%

c. 288 in² of the piece of stock costs $12.00,

Each cut-out circle of 113.04 in² (226.08/2) will cost = (12*113.04)/288

= 1,356.48/288 = $4.71.

3 0
4 years ago
Robin and Meg are traveling from New York to Florida, and plan to stop at three different campgrounds along the way. After choos
matrenka [14]

You are correct. For each of the three possibilities for their second day, there are two possibilities for the third day.

The total number of possibilities is 3*2 = 6.

6 0
3 years ago
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