Thinking Mathematically (6th Edition)

Published by Pearson
ISBN 10: 0321867327
ISBN 13: 978-0-32186-732-2

Chapter 1 - Problem Solving and Critical Thinking - 1.3 Problem Solving - Exercise Set 1.3: 68

Answer

19 rungs

Work Step by Step

The firefighter started on the middle rung. (I drew this problem out just labeled it “middle” to start). He climbed up 4 rungs. I labeled the rung above the middle as “1” and went up from there to “4”. We know there is a middle rung plus 4 rungs above it. He then went down 6 rungs. (The first 4 he went down took him back to middle), then the next two (so that he went down 6 rungs) put him 2 below the middle. He then climbed up 7 rungs and stayed until the fire was out. The first 2 rungs took him to the middle rung. Then to finish going up the 7 rungs, he ended up 5 rungs above the middle one. Last, he climbed up 4 more rungs and entered the building. He was already 5 above the middle, so going up four more rungs put him 9 above the middle. There were 9 rungs above the middle rung and 9 rungs below the middle rung. And, we must also count the middle rung. 9 plus 9 plus 1 is 19.
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