<s>[INST] mixed numbers subtraction vertically In the following subtraction we are subtracting $2$ mixed numbers vertically. I know how it works except the last step.
$$ 7 \frac{1}{3} - 4 \frac{1}{2} = 3 + \frac{-1}{6} = 2 + \frac{5}{6} = 2 \frac{5}{6}$$
I am confused about this step: $ 3 + \frac{-1}{6} = 2 + \frac{5}{6}$
How does this work? 
 [/INST] For "normal" subtraction, we all learned in elementary school to "borrow" a 1 from the next highest place if we needed to.
In this case, we're sort of doing the same thing. When we have $3 + -1/6$, we "borrow" a 1 to make $2 + 6/6 + -1/6$, which then becomes $2 + 5/6$.
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