Bill Gates doesn't know how much Rice-A-Roni costs

Talk-show host Ellen DeGeneres quizzes the Microsoft co-founder on grocery store prices. Man knows his dental floss.

Face it: Billionaire Microsoft co-founder Bill Gates doesn't really need to look at prices. So when he appeared on "The Ellen DeGeneres Show" on Tuesday, DeGeneres put his big grain to the test, playing a sort of "Price is Right" game she dubbed "Bill's Grocery Bills."

Gates admitted he hadn't been to a supermarket in a while, and he proved it on his first guess, when he surmised that a $1 box of Rice-A-Roni costs $5. We're guessing the packaged rice mix isn't served much in Gates' $100-plus million Lake Washington estate near Seattle.

Gates also had to guess the prices of Tide Pods, dental floss, Totino's Pizza Rolls, and TGI Friday's frozen artichoke dip. Gates must keep his teeth in good shape, because he knew the cost of floss better than anything. (Also, these must be Hollywood prices, because some of them seemed kinda high for where the rest of us live.)

The show also shared a video of DeGeneres interviewing Gates, in which he discusses his indoor trampoline room, becoming a billionaire at 21, and the work of the Bill & Melinda Gates Foundation.