Algebra 2 (1st Edition)

Published by McDougal Littell
ISBN 10: 0618595414
ISBN 13: 978-0-61859-541-9

Chapter 1, Equations and Inequalities - 1.2 Evaluate and Simplify Algebraic Expressions - 1.2 Exercises - Problem Solving - Page 15: 60


See below.

Work Step by Step

Let $x$ be the number of minutes spent running ($0\leq x\leq60$). Then the number of minutes spent walking is: $60-x$. Then the amount of calories burnt if we run $x$ minutes is: $f(x)=x\cdot10+(60-x)\cdot4=10x+240-4x=240+6x$. Thus if we walk $20$ minutes and then run $40$, the number of burnt calories is: $f(40)=240+6\cdot40=240+240=480$
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