# Tutor profile: Mary R.

## Questions

### Subject: R Programming

How do I use the lm() function?

The lm() function is the easiest way to do a linear regression. The function works like this: my.regression <- lm(dependent.variable ~ indep.var.1 + indep.var.2 + indep.var3, data = mydata) This is a simple regression showing how three independent variables affect the dependent variable! I think of the ~ as saying "is affected by". You can then use the command summary(my.regression) to get the regression coefficients! Easy peasy.

### Subject: College Admissions

How do I decide what to write about in my Common App essay?

My first word of advice is to write about something that you're really passionate about, something that, while it might be small, you really care about. Use this essay to highlight something that makes you a great candidate for every school. For example, I wrote about how tall traffic lights are. I used my quest to find out traffic lights' heights as an example of how I will search for answers until I can find one. The most successful Common App essays are those that sell yourself as a candidate and demonstrate your passion in something that isn't represented in the rest of your application.

### Subject: Economics

What is the property of diminishing marginal returns?

Let's think of an example. When one person uses a shovel, he can shovel pretty well? But what if TWO people use one shovel? Their productivity goes way down, because there are too many people using too little equipment. That's a simple example of diminishing marginal returns! Let's think of a harder example. Assume that one factor of production (a donut machine) is fixed. We only have one. With one person running it, you maybe 2 donuts made in an hour. With two people, you get, lets say, 10 donuts. Three, 15. Four, 18. Five, 20. While you are getting more donuts overall, each person is only adding a few more donuts to total output. The second man increases the donut count by 8. The third by 5. The fourth by 3. The fifth by 2. And so on! This is diminishing marginal returns.

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