Answer:
140
Step-by-step explanation:
To construct a subset of S with said property, we have two choices, include 3 in the subset or include four in the subset. These events are mutually exclusive because 3 and 4 can not both be elements of the subset.
First, let's count the number of subsets that contain the element 3.
Any of such subsets has five elements, but since 3 is already an element, we only have to select four elements to complete it. The four elements must be different from 3 and 4 (3 cannot be selected twice and the condition does not allow to select 4), so there are eight elements to select from. The number of ways of doing this is
.
Now, let's count the number of subsets that contain the element 4.
4 is already an element thus we have to select other four elements . The four elements must be different from 3 and 4 (4 cannot be selected twice and the condition does not allow to select 3), so there are eight elements to select from, so this can be done in
ways.
We conclude that there are 70+70=140 required subsets of S.
I would say, the best way and the fastest way, is to go to some banks and ask them how much interests they give you... then the bank that gives you the most interest, the bank that you are looking for.
D.) It is not correct because the second number tells you how far to go up or down, not across.
Second number represents y-coordinates, so they are the points in vertical direction, in that case you can't move in x-axis which is horizontal.
Hope this helps!