# Tutor profile: Lisa S.

## Questions

### Subject: GRE

If 4x + 20 = 40 - x, what is the value of x?

The easiest way to solve this equation is to move the "x" terms to the same side, and the non-"x" terms to the other side. You can first move the "x" on the right side of the equation to the left side by adding "x" to each side of the equation. You now have 5x + 20 = 40. You can then subtract 20 from both sides of the equation, which gives you 5x = 20. You can then divide each side by 5, giving you x = 20/5 = 4. Therefore, the value of x is 4!

### Subject: Psychology

What are different methods that can be used to select a sample for your research study?

There are many different methods that you could use to select a sample for your research study, each with different considerations. Here are some common sampling techniques: 1) In random sampling, each individual in the population has an equal chance of being selected. 2) In stratified sampling, a sample can be designed to be representative across a variable- for example, if you stratify by gender, you can design your sample to be 50% women and 50% men. 3) Opportunity/convenience sampling: you use participants who are available and willing to participate- for example, students in your psychology class! 4) Systematic sampling: you create a system for choosing participants; for example, you dial every 10th phone number in a phone book.

### Subject: Statistics

What is the central limit theorem in statistics?

The central limit theorem proposes that the distribution of sample means (or averages), under many circumstances, will be a normally distributed "bell curve." To obtain a distribution of sample means, you basically would collect several observations (for example, the percentage of times a coin landed on "head"). You may get 40% as an average for the first time. You would then repeat this experiment many times to get many different averages. The central limit theorem says that if you do this an infinite number of times, you will obtain a normally distributed curve.

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