Sweet dreams of chocolate and mathematics

I often that find articulating my dreams to others is a frustrating endeavor because its so difficult to convey the realism without sounding overly passionate. But this is more about dreams in general than the content of my particular dream.

I was at a restaurant in Brasil and was offered some chocolates by a candy vendor who was, incedentally, a sweet, intelligent friend from high school named Katelyn Keefe... hey, dreams are weird. The price was $0.78 for one type and $0.83 for another. I decided, out of pity for my unsucessful colleague, to purchase 5 of each. Arthimetic gives 5*($0.78+$0.83)=$8.05. The cashier in the group (it took three people to sell me a handful of chocolate), asked for "dez reai" which I assumed meant "dez reais" or R$10. I obliged.

I should note that I did not do the calculation of the cost precisely in my dream. In fact, I am wondering if it is even possible to do a problem of this "complexity" in a dream. I knew in the dream that it was going to be less than $10, simply because 10 items for under $1 each will be less than $10. So I had some general deductive powers, but I'm not sure if I had particular mathematical powers. If I were better at mental math would I have been able to do it? Can you use pen and paper in a dream?

In short I felt in the dream as if I deserved change, but the cashier was not forthcoming. Did my friend rip me off? Or was there some unspoken tax? I guess we'll never know because those are questions that can only be answered in terms relative to the particular dream (unless you believe there are universal dream laws...which I highly doubt).

And to top it off it was diet chocolate so I ended up giving it away. Hey, diet chocolate stinks in dreams too!