###Human: A milk teas shop was able to sell a total of 50 cups of milk tea yesterday. Two-fifths of their sales are winter melon flavor, three-tenths are Okinawa flavor, and the rest are chocolate flavor. How many cups of chocolate-flavored milk tea were they able to sell yesterday?, ### Assistant: A milk tea shop sold 50 x 2/5 = 20 cups of winter melon-flavored milk tea.
They sold 50 x 3/10 = 15 cups of Okinawa-flavored milk tea.
So they sold a total of 20 + 15 = 35 cups of winter melon and Okinawa flavors milk tea.
Therefore, they sold 50 - 35 = 15 cups of chocolate-flavored milk tea. 
 So the answer is :  15