With this sort of problem, you want to write two equations that are equal to each other that keep the overarching proportions equivalent.
The numerator and the denominator should represent the same basic thing.
So, here, each equations should take the form:
(Serving / Calories)
So, set the equations equal to one another, where
2 servings = 5 servings
310 calories c calories
The way you could read this is, "If 2 servings is equivalent to 310 calories, then 5 servings is equivalent to c calories"
You solve this sort of problem by cross-multiplying, meaning that you multiply the numerator (top) of one equation by the denominator (bottom) of the other.
So,
2 servings * c calories = 5 servings * 310 calories
Now, solve for c:
2c = 5 * 310
2c = 1550
c = 775 calories
Another way you could solve this problem is to think about / solve how many calories one serving is equivalent.
If 2 servings = 310 calories, then one serving = 310/2 = 155 calories.
Then, to calculate how many calories 5 servings is, you could multiply 5 * 155 = 775.
