Hello there! There are 9 servings in 15 cups.
Since there is a constant rate, the rate will always be the same, so whatever you multiply one of the values in the ratio by, you can multiply the other value by, and get an accurate result.
Here's how we use this to solve the equation you gave:
3 servings is 5 cups can be displayed in ratio form as 3:5, 3 being the number of servings with 5 cups.
If we have 15 cups and an unknown servings value, we have the ratio x:15. We can take whatever we multiplied 5 by to get 15 and multiply it by 3 to get our servings amount. To find this, divide 15 by 5. 15/5 = 3.
With this information, we can multiply 3 x the three servings and we get a total of 9 servings. I hope this helps and have a great rest of your day! :)