this sounds a lot like the right versus left brain in dreaming from another topic.

Visual dreams are primarily right-brained, and the left-brain is barely involved. Since the left brain is responsible for telling time, reading and MATH, that would explain why you couldn't add up the numbers, or read in other dreams.

Whenever i "read" in my dreams, I'm usually looking at a book, and the ideas of the words or sentences enter my brain... i'm not actually reading words at all. It sounds the same way with you and math. You know how much money is there, but aren't sure how to get there without that left-brain.