Turn the mixed numbers into improper fractions first.
2 1/3 = 7/3
1 3/4 = 7/4
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Now add the fractions
7/3 + 7/4
Find the common denominator by multiplying
7 x 4 7 x 3 49
------- + -------- = -----
3 x 4 4 x 3 12
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Now convert to a mixed number
49/12 = 4 and 1/12 is your answer