You could certainly leave the comma out and some would say it is incorrect. Here, other errors rule out the rest of the choices. I probably wouldn't use it, but sometimes it is helpful when the objects listed are complex phrases rather than simple nouns.

median is the one in the middle when the terms are put in numerical order. When you have an odd number of items, it will be the middle one. When you have an even number it will be the average between the two middle terms. Mean is the arithmetic average, i.e. the sum of the terms divided by the numbe...

To be divisible by 12, n must be divisible by 2 twice plus 3. 1) To be divisible by 6, n must be divisible by 2 and 3. - doesn't tell us that we can divide by 2 twice 2) to be divisible by 4, n must be divisible by 2 twice - doesn't tell us that n is divisible by three combining, n must be divisible...

There may be a more sophisticated way to solve this, but the following worked for me. First I solved for a^2, b^2 and c^2 and added them and got: -14 - 6a - 2b - 4c That tells me that the answer must be even so it has to be a or c. Since our answers are integers I assume the variables are integers. ...

AS shown above:
the mode is unchanged
the median is unchanged
the mean decreases

Answer C

If you have 33 students, the mean of whose ages is 13 and you remove three students, one 18, one 17 and one 5 years old, you use the average formula. The sum of the terms divided by the number of terms = the average. In the original case we do not know the sum, so we will use S. Our formula becomes ...

What is the source of this problem. The stimulus doesn't make sense. What is meant by "4 miles of Midway"?

The "and that" in C implies that the theory contributed to the extinction of the dinosaurs.