Discrete Mathematics with Applications 4th Edition

Published by Cengage Learning
ISBN 10: 0-49539-132-8
ISBN 13: 978-0-49539-132-6

Chapter 5 - Sequences, Mathematical Induction, and Recursion - Exercise Set 5.7 - Page 315: 20

Answer

$2$ minutes $18$ seconds

Work Step by Step

First, convert 3 minutes to seconds: \[ 3 \text{ minutes} = 3 \times 60 = 180 \text{ seconds}. \] Since she improves (reduces) her time by 3 seconds each day, we have an arithmetic sequence: \[ T_n = T_0 - 3n, \] where \(T_0 = 180\) seconds (her time on day 0) and \(T_n\) is her time (in seconds) on day \(n\). On day 14, \[ T_{14} = 180 - 3 \times 14 = 180 - 42 = 138 \text{ seconds}. \] To convert back to minutes and seconds: \[ 138 \text{ seconds} = 2 \text{ minutes and } 18 \text{ seconds}. \]
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