Math 111
posted by Joey .
This is a question that deals specifically with WebWork.
Here is the question:
Write the set of points from 2 to 4 but excluding 1 and 4 as a union of intervals
my solution to this would be: [2,4]U(1,4)
my reasoning:
The first set includes 2 and goes up to and includes 4, the second includes everything greater than 1 and goes to everything less than 4. This way, the integer 2 is still included. BUT, this is wrong.

If you had all the points, you'd have [2,4]
But, you have to exclude 4, leaving [2,4)
Now, inside this interval, you exclude 1, so you have to break it up into two intervals:
[2,1)U(1,4) 
Write the set of points from 5 to 1 but excluding 4 and 1 as a union of intervals

(5,1)U(4,1)