3 yuan -6 yuan. McDonald's colas are: 300ml small 7 yuan, 400ml medium 9 yuan, 500ml large 1 1 yuan. The cost of cups is one in 0.5 yuan, the wholesale price of a barrel of 500ml cola is 6 yuan, and the cost of McDonald's cola is in 3 yuan -6 yuan. Small cups have low cost and high profit, while large cups have high cost and high profit. McDonald's is a large multinational chain restaurant in the world, mainly selling hamburgers and French fries, fried chicken, soda, ice products, salads, fruits and other fast food.