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Ivanshal [37]
1 year ago
15

1. A notebook costs $5 more than a folder. Greg purchased 3 notebooks and 2 folders and paid a total cost $30. What is the cost

of each item? 1. A notebook costs $ 5 more than a folder . Greg purchased 3 notebooks and 2 folders and paid a total cost $ 30 . What is the cost of each item ?​
Mathematics
1 answer:
stiv31 [10]1 year ago
8 0
Answer
Notebook each =$4
Folder each = $9

First we write out what we know
Notebook = n
Folder = f
It says a notebook is +5 than a folder so
f = n +5
It says he bought 3 notebooks and 2 folders for $30
3n + 2f = 30

Because we know from the first equation
f=n+5, we can substitute that into the second equation for f

3n + 2(n+5) = 30
3n + 2n +10 =30. Now Combine like terms
5n +10 =30. Now isolate n by subtracting 10 from both sides
5n = 20. Now isolate n by dividing both sides by 5
n = 4

Now we do the same thing to find f
We substitute the value of n (4) into the equation 3n + 2f =30
3(4) +2f =30
12 +2f =30. Now isolate f by subtracting 12 from both sides
2f = 18. Now isolate f by dividing both sides by 2
f = 9


We check our work by inserting the n and f values we found into one of the equations
n + 5 = f
4 + 5 = 9
9 = 9. It worked it equals so it’s correct
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So the value of height that separates the bottom 85% of data from the top 15% is 38.32.  

C) 38.32

Step-by-step explanation:

1) Previous concepts

Normal distribution, is a "probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean".

The Z-score is "a numerical measurement used in statistics of a value's relationship to the mean (average) of a group of values, measured in terms of standard deviations from the mean".  

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X \sim N(30,8)  

Where \mu=30 and \sigma=8

And the best way to solve this problem is using the normal standard distribution and the z score given by:

z=\frac{x-\mu}{\sigma}

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P(X>a)=0.15   (a)

P(X   (b)

Both conditions are equivalent on this case. We can use the z score again in order to find the value a.  

As we can see on the figure attached the z value that satisfy the condition with 0.85 of the area on the left and 0.15 of the area on the right it's z=1.04. On this case P(Z<1.04)=0.85 and P(z>1.04)=0.15

If we use condition (b) from previous we have this:

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But we know which value of z satisfy the previous equation so then we can do this:

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And if we solve for a we got

a=30 +1.04*8=38.32

So the value of height that separates the bottom 85% of data from the top 15% is 38.32.  

C) 38.32

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