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? Let's think first. Chain of thought:
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.
Therefore, the answer is 15.