Basic College Mathematics (10th Edition)

Published by Pearson
ISBN 10: 0134467795
ISBN 13: 978-0-13446-779-5

Chapter 2 - Multiplying and Dividing Fractions - 2.6 Applications of Multiplication - 2.6 Exercises - Page 158: 29


The correct answer is $\frac{6}{7}$.

Work Step by Step

The student's error is in the step where he attempted to reduce the fractions by the common factor 3. The denominator of $\frac{20}{21}$ should have been changed to 7 ($21 \div 3$), not 3. This would have resulted in the following equation: $\frac{9}{10} \times \frac{20}{21}$ = $\frac{3}{1} \times \frac{2}{7}$ = $\frac{6}{7}$
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