Question

The output is one less than twice the size the imput

Answer 1

If the output equals o, and the input equals i, the equation would be o = 2i - 1, because twice the size of the input is 2i, one less than is -1, and o is the output.

Answer 2

o = 2i - 1
o = output
2 i = twice the input
then -1 = one less