3 1⁄8 − 1 7⁄8 = as a mixed number
3 1/8 can be written as 2 9/8
so 3 1/8 - 1 7/8 → 2 9/8 - 1 7/8 → (2-1) + (9/8 - 7/8) → 1 2/8 → 1 1/4
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