DeGeneres decided to put the billionaire Microsoft co-founder to the test by asking him to guess the price of common grocery store items such as boxed rice, laundry detergent pods, floss and pizza rolls.
The stakes: If he guessed the prices within a dollar for at least three of the products, every audience member would win a prize.
But Gates' first try didn't bode well for the audience. "How much do you think Rice-A-Roni would be, within a dollar?" Degeneres asked.
"Five dollars," Gates guessed before noting, "the audience didn't like that [answer]." The correct price: only $1.
With some hints from the audience, Gates was able to adjust his responses and come up on the right side of a few other products. Eventually he guessed three out of five correctly and sent the audience home with a chance to return to the show for one of DeGeneres's Twelve Days of Giveaways in December.
But his initial guesses were telling: He predicted that a bag of frozen pizza rolls might be $22 while an eight-ounce container of spinach and artichoke dip couldn't be under $10. Both were actually far less.
Here's how Gates fared on the quiz:
Gates's answer: $5
Correct answer: $1
Gates's answer: $10
Correct answer: $19.97
Gates's answer: $4
Correct answer: $3.78
Totino's pizza rolls
Gates's answer: $8
Correct answer: $8.98
T.G.I. Friday's spinach and artichoke dip
Gates's answer: $4
Correct answer: $3.66
He may be out of touch with what regular consumers pay at the grocery store, but Gates is committed to staying abreast of the issues of wealth inequality worldwide. Alongside his wife, Gates works full time on the Bill and Melinda Gates Foundation, which spends more than $4 billion per year fighting disease, improving education, distributing vaccines and battling inequality across the globe.
Gates also says that a greater portion of his fortune should go back into the government. "I need to pay higher taxes," he told CNN's Fareed Zakaria during a recent interview. "I've paid more taxes, over $10 billion, than anyone else, but the government should require people in my position to pay significantly higher taxes."
Like this story? Like CNBC Make It on Facebook!