Regarding the concept. . .Just keep this in mind:

An effect arising between two or more agents, entities, factors, or substances that produces an effect greater than the sum of their individual effects. It is opposite of antagonism. See also synergism.

So, two can be 2.5 or 3. . 3 can be 7.5 to 10 just depending.

One, with the right tools can be self sufficient. . Under the right circumstances.

And ultimately, 3 people in the desert with No water and no skill. . .still doomed.