What can add up to 5.778?

Answer 1

An infinte number of pair of numbers, and an infinite number of triplets, and an infinite number of quartets etc.

For pairs consider:

... , -1 and 6.778, 0 and 5.778, 1 and 4.778, 2 and 3.778, ...

and

..., -0.9 and 6.678, 0.1 and 5.678 and 1.1 and 4.678, ...

and

..., -0.8 and 6.578 etc

and then you can go two the second decimal place.

Also, use Irrational Numbers.

In fact if A is ANY number, then let B = 5.778-A

and then A + B = 5.778

So for every number, rational, irrational, complex or otherwise, there is another so that the two add to 5.778.