That's part of "the trick."
Most of us can subconsciously count in base 10 very, very quickly. In the question, the number 1.00 is a simple multiple of .10. Very base 10.
This means that you subconsciously "process" the equation. In other words, you aren't consciously paying attention to how, exactly, you arrive at the answer you want to instantly blurt out (this urge to "blurt out" the wrong answer is a definite signal of subconscious processing).
If you processed it consciously, you'd much less likely to skip over the meaning of "$1.00 more than."
Also, since this seems to be simple base 10 math, your subconscious expectation is that there will be a simple base 10 answer - $1.00 + .10 "seems" or "feels" like a better answer than $1.05 + .05.
Ugh... Math. I've never been great at math. I, of course, did the obvious but wrong answer first but I do get it... Or I get it some of the time I think about it, other times I don't. D: lol
)
