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Evaluate.

4C2 =

6

Step-by-step explanation:

₄C₂ means that we're trying to see how many ways we can pick 2 things out of a group of 4. We have 4 options for our first pick and 3 for our second, so that gives us a total of 4 · 3 = 12 ways of choosing.

Now, the "C" in ₄C₂ is short for "combinations." Order doesn't matter where combinations are concerned. Let's say the set we're choosing from is the set of the letters A, B, C, and D. Here are all the ways we can choose two different letters from that list:

AB, AC, AD, BA, BC, BD, CA, CB, CD, DA, DB, DC

Notice that, for each pair, we have another in the set that contains the same letters: AB and BA, AC and CA, BD and DB... If order doesn't matter, we can cut all of those second pairs, giving us 12 / 2  = 6 total combinations.

a. the residual plot for model 1 has a random pattern and is a good fit for the data.