Answer:

And replacing we got:

And then the estimator for the standard error is given by:

Step-by-step explanation:
For this case we have the following dataset given:
20.05, 20.56, 20.72, and 20.43
We can assume that the distribution for the sample mean is given by:

And the standard error for this case would be:

And we can estimate the deviation with the sample deviation:

And replacing we got:

And then the estimator for the standard error is given by:

I have 0 idea but I need help with some questions that I have
Answer:
120x^3y^7
We can use the Pascal's triangle to solve this question.
This pascal's triangle is shown in the Image below. To build the triangle, begin with the number 1 at the top, then continue placing numbers below it in a triangular pattern. In this way, each number are the numbers directly above added together. So, the expression is :
(x+y)10
After you do the steps you be left with:
120x^3y^7