Elementary Algebra

Published by Cengage Learning
ISBN 10: 1285194055
ISBN 13: 978-1-28519-405-9

Appendix - Extra Word Problems: 116

Answer

80 minutes

Work Step by Step

Let t be the time it takes with the power mower. Thus: $ 1 = \frac{20}{t} + \frac{30}{t-40} $ We create common denominators to obtain: $ 1 = \frac{30t+20t-800}{t(t-40)} \\ 30t+20t-800 = t^2 - 40t \\ t^2 -90t + 800 = 0 \\ (t-80)(t-10)$ Since she already took 30 minutes, 10 minutes does not make sense. Thus, the answer is: 80 minutes.
Update this answer!

You can help us out by revising, improving and updating this answer.

Update this answer

After you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.