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oobleck since both of those fractions are close to 1, a first guess might be
1 x 1 = 1
not really very good, since it's actually 32/45 ≈ 3/4
maybe a better estimate would be (since 9≈10)
4/5 * 8/10 = 4/5 * 4/5 = 16/25 ≈ 16/24 = 2/3
you don't say how accurate you want to be.