
has ten elements, so any proper subset has at most nine of these elements.
The number of ways of taking any

letters from this set is given by the binomial coefficient,

and in particular, the total number of ways to picking proper subsets is

Without computing each term directly, let's instead use a direct result from the binomial theorem, which says

If we replace

, then we're left with

We can use this to evaluate our sum directly:
Plug the numbers and see if they fit
Answer:

Step-by-step explanation:
Pythagorean Theorem: In the right triangle the square of longer side is equal to the sum of the squares of other sides.

Answer:
m = 5/6
Step-by-step explanation:
Cross multiply.
1/5 × m = 2/3 × 1/4
1/5 × m = 2/12
1/5 × m = 1/6
m = 5/6