Basic College Mathematics (10th Edition)

Published by Pearson
ISBN 10:
ISBN 13:

Chapter 3 - Adding and Subtracting Fractions - 3.4 Adding and Subtracting Mixed Numbers - 3.4 Exercises - Page 229: 34

Answer

Estimated answer = 9 Exact answer = $8\frac{2}{15}$

Work Step by Step

$20\frac{3}{5}$ - $12\frac{7}{15}$ Estimation: $20\frac{3}{5} \approx 21$ $12\frac{7}{15} \approx 12$ Therefore $20\frac{3}{5}$ - $12\frac{7}{15}$ $\approx$ 21 - 12 = 9 Exact Calculation: $20\frac{3}{5}$ - $12\frac{7}{15}$ = $20\frac{3\times3}{5\times3}$ - $12\frac{7}{15}$ (15 is the least common denominator) = $20\frac{9}{15}$ - $12\frac{7}{15}$ = ($20$ - $12$) + ($\frac{9}{15}$ - $\frac{7}{15}$) (Solving whole parts separately and fractional parts separately) = $8$ + $\frac{9 - 7}{15}$ = $8$ + $\frac{2}{15}$ = $8\frac{2}{15}$ The estimate was 9, so the exact answer of $8\frac{2}{15}$ is reasonable.
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