Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 1 - Section 1.7 - Modeling with Equations - 1.7 Exercises - Page 78: 73

Answer

240 or 50 mi/h

Work Step by Step

Time it takes from Ajax to Barrington : x Time it takes from Barrington to Collins : x+6minutes =x+$\frac{1}{10}$h Speed from Ajax to Barrington :s x=$\frac{120}{s}$ x+$\frac{1}{10}$=$\frac{150}{s+10}$ $\frac{120}{s}$+$\frac{1}{10}$=$\frac{150}{s+10}$ multipy by 10s(s+10) 1200(s+10)+s(s+10)=10s(150) 1200s+12000+$s^{2}$ +10s=1500s $s^{2}$ -290s+12000=0 Quadratic formula: $290^{2}$-4$\times$12000=36100 s=$\frac{290+or-191}{2}$ s=50 or 240
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