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3 years ago

This is really difficult for me. If someone could help me I would really appreciate it.

Mathematics

2 answers:

-Dominant- [34]3 years ago

4 0

Since we can add up the factors of 28 (excluding 28 itself) to get
1+2+4+7+14 = 28
this means that 28 is a perfect number. In the interval from 20 to 30, it is the only perfect number.

Answer: 28

Note: Something like 22 is not a perfect number since
1+2+11 = 14
which isn't 22 like we want. Every number, in the interval from 20 to 30, but 28 has this problem.

Dmitrij [34]3 years ago

3 0

<span>20, 21, 22, 24, 25, 26, 27, 28, 30. hope that helped</span>

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3 years ago

Consider the relationship between the number of bids an item on eBay received and the item's selling price. The following is a s

n200080 [17]

Answer:

Let's assume the following data:

Price in Dollars (X) 26 29 32 38 47

Number of Bids (Y) 12 13 15 16 18

For our case we have this:

n=10 $\sum x = 172, \sum y = 74, \sum xy = 2623, \sum x^2 =6194, \sum y^2 =1118$

$r=\frac{5(2623)-(172)(74)}{\sqrt{[5(6194) -(172)^2][5(1118) -(74)^2]}}=0.974$

So then the correlation coefficient would be r =0.974

Step-by-step explanation:

Previous concepts

The correlation coefficient is a "statistical measure that calculates the strength of the relationship between the relative movements of two variables". It's denoted by r and its always between -1 and 1.

Solution to the problem

And in order to calculate the correlation coefficient we can use this formula:

$r=\frac{n(\sum xy)-(\sum x)(\sum y)}{\sqrt{[n\sum x^2 -(\sum x)^2][n\sum y^2 -(\sum y)^2]}}$

Let's assume the following data

Price in Dollars (X) 26 29 32 38 47

Number of Bids (Y) 12 13 15 16 18

For our case we have this:

n=10 $\sum x = 172, \sum y = 74, \sum xy = 2623, \sum x^2 =6194, \sum y^2 =1118$

$r=\frac{5(2623)-(172)(74)}{\sqrt{[5(6194) -(172)^2][5(1118) -(74)^2]}}=0.974$

So then the correlation coefficient would be r =0.974

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3 years ago