Answer:

Step-by-step explanation:
1 n=0
1 1 n=1
1 2 1 n=2
1 3 3 1 n=3
1 4 6 4 1 n=4
1 5 10 10 5 1 n=5
1 6 15 20 15 6 1 n=6
This is where n is the exponent in
.

Now we want to expand:
or we we can rewrite as
.
Let's replace
with
and
with
in the expansion:



Let's simplify a bit:


You question implies simple subtraction is needed:
28-8=20
Answer:
<em>Choose the first alternative</em>

Step-by-step explanation:
<u>Probabilities</u>
The requested probability can be computed as the ratio between the number of ways to choose two sophomores in alternate positions
and the total number of possible choices
, i.e.

There are 6 sophomores and 14 freshmen to choose from each separate set. There are 20 students in total
We'll assume the positions of the selections are NOT significative, i.e. student A/student B is the same as student B/student A.
To choose 2 sophomores out of the 6 available, the first position has 6 elements to choose from, the second has now only 5

The total number of possible choices is

The probability is then

Choose the first alternative