3 Answers

You have to multiple by the reciprocal.
(5/8) / (15/16) = (5/8)(16/15) = (80/120) = 2/3

You can not divide fractions so you must flip the second fraction around and multiply:
5/8 x 16/15
Now simply multiply the top and bottom numbers into each other:
80/120
Simplify the fraction as much as possible:
2/3
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You can also simplify the fractions before multiplying (remember you can only simplify vertically or diagonally, NEVER horizontally):
5/8 x 16/15
Simplify the 8 and 16:
5/1 x 2/15
Simplify the 15 and 5:
1/1 x 2/3
2/3

80/120=2/3