He is a 'wizard' at math.
a math 'wizard'
(..) I said, "These are new tires." "Why don't you throw in something else, like your wife?" His wife was Miss New Jersey . That's why the fleet has no spares. Doughboy, wizard, killer. - Charlie T. - What's happening? Travis, you got a fare. Shit. - See you later. (..)1976 Taxi Driver
(..) You better take your ass out, boy! - Yeah? - I know you and I ain't talked too much. But I figured you've been around a lot. So you could... Shoot, that's why they call me the "Wizard." It's just that I got a... - I got a... - Things got you down? - Yeah. - It happens to the best of us. (..)1976 Taxi Driver