# Tutor profile: Lulu Y.

## Questions

### Subject: SAS

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

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

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

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

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?

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

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