Count all trues in truth tables

Let's just say you have a variable that contains either true or false, well, we're talking about truth tables aren't we?
The combinations
Var A
+-------+
| true |
+-------+
| false |
+-------+
Var A Var B
+-------+-------+
| true | true |
+-------+-------+
| true | false |
+-------+-------+
| false | true |
+-------+-------+
| false | false |
+-------+-------+
Var A Var B Var C
+-------+-------+-------+
| true | true | true |
+-------+-------+-------+
| true | true | false |
+-------+-------+-------+
| true | false | true |
+-------+-------+-------+
| true | false | false |
+-------+-------+-------+
| false | true | true |
+-------+-------+-------+
| false | true | false |
+-------+-------+-------+
| false | false | true |
+-------+-------+-------+
| false | false | false |
+-------+-------+-------+
You see where this is going? Truth tables basically gives a representation of possible combinations of truths and lies (I mean true and false :/).
Count all combinations
So how do we count all combinations of true and false?
Let's say variable is called v
.
Let's say true and false is a pair (2).
Let's say a variable can contain either true or false.
Let's say we have 1 variable:
2 total combinations of true and false
Let's say we have 2 variables:
8 total combinations of true and false
Count only true
(or false
)
So how do we count all true
occurences? it's simple, we half the total.
We already know that e.g. 2 variables have a total combination of 8.
So that's 4 true
s (and 4 false
s also).