How many ways can 20 be obtained from the sum of 8 numbers?

Answer 1

Infinitely many.

1 + 1 + 1 + 1 + 1 + 1 + 1 + 13

1 + 1 + 1 + 1 + 1 + 1 +1.1 + 12.9

1 + 1 + 1 + 1 + 1 + 1 +1.2 + 12.8

and so on.

And then I can start looking at 2-digit decimals, and then 3.

And then vary the sixth number, and then the fifth,

And that is only the rationals. I can add irrationals to the list of numbers.

Finally, there is no requirement (in the question) for the numbers to be positive.