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# Tutor profile: Lulu Y.

Inactive
Lulu Y.
Statistical Programmer for a Top 20 Pharmaceutical Company
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## Questions

### Subject:SAS

TutorMe
Question:

What is the difference of "PROC SORT NODUP " and "PROC SORT NODUPKEY"?

Inactive
Lulu Y.

NODUP will delete the observations which are exactly the same in all variables. NODUPKEY will delete the observations which are identical in the "BY" variable(s).

### Subject:Calculus

TutorMe
Question:

When we want to know a maximum value of a curve, y = 5+ x^2 (x square), what is the solution by using derivative?

Inactive
Lulu Y.

Find the derivative of y = 5+ x^2 , which is 2*x, and when this equals to 0, we have the max value of y

### Subject:Statistics

TutorMe
Question:

When we are using t-test to compare the mean of two groups, for example, we want to find out, whether there is a significant difference in the height of two groups of girls. What assumption we need before we are using t-test?

Inactive
Lulu Y.

The mean of the height of two groups is asymptoticly normally distributed.

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