“If you increase it one whole time- it equals 2”
“Multiply” is not a synonym for “increase”. If I multiply something by zero, it only increases if the original was negative. If I multiply something by a negative, again, it can only increase if the original was negative.
Multiply Definition & Meaning - Merriam-Webster
Definition of multiply. (Entry 1 of 3) transitive verb. 1 : to increase in number especially greatly or in multiples
And again,
transitive verb
1a : to become greater in number :
That there are other definitions as well doesn’t negate the fact that it also means to increase in number— -