(-2 1/2)×(-3 1/2) = (2 1/2)×(3 1/2) . . . . deal with the signs up front. The product of two negatives is a positive.
... = 2×(3 1/2) + (1/2)×(3 1/2) . . . . . use the distributive property
... = 2×3 + 2×(1/2) + (1/2)×3 + (1/2)×(1/2) . . . . and again
... = 6 + 1 + 3/2 + 1/4
... = 7 + (1 1/2) + 1/4
... = 8 + 2/4 + 1/4
... = 8 3/4
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On your calculator, -2.5 × -3.5 = 8.75.