Answer: 4 servings
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Step-by-step explanation:
It might help to imagine that you had a measuring spoon that is 1/3 cup. Note how exactly three of them gets you to a full cup since 3*(1/3) = 3/3 = 1.
Adding another helping of the measuring spoon gets you to the mixed number of 1 & 1/3. This is because the mixed number 1 & 1/3 is identical to the math expression 1 + (1/3). We add the fractional portion 1/3 on top of the whole number 1. That's why the verbal form of this is "one and one-third". The "and" says "add" more or less.
In short, we need 3 servings to get to one full cup. Then that fourth serving will get us to 1 & 1/3 cup.