Algebra Demystified 2nd Ed

Chapter 8 linear appliCaTionS 291

A jet leaves Dallas going to Houston, averaging at 400 mph. At the same

time, another jet leaves Houston, flying to Dallas, at the same rate. How

long will it take for the two planes to meet? (Dallas and Houston are

250 miles apart.)

The distance between the jets is decreasing at the rate of 400 + 400 =

800 mph. Let t represent the number of hours they are flying.

800 250

250

800

5

16

t

t

t

=

=

=

The planes will meet after 165 hours or (^60) () 165  =  1834 minutes or 18 minutes
45 seconds.
PRACTICE

1. Jessie leaves her house on bicycle, traveling at 8 mph. She is going to
   her friend Kerrie’s house. Coincidentally, Kerrie leaves her house at the
   same time and rides her bicycle at 7 mph to Jessie’s house. If they live
   5 miles apart, how long will it take for the girls to meet?


2. Two cars 270 miles apart enter an interstate highway traveling toward
   one another. One car travels at 65 mph and the other at 55 mph. When
   will they meet?


3. At one end of town, a jogger jogs southward at the rate of 6 mph. At the
   opposite end of town, at the same time, another jogger heads north-
   ward at the rate of 9 mph. If the joggers are 9 miles apart, how long will
   it take for them to meet?

✔SOLUTIONS

1. The distance between the girls is decreasing at the rate of 8 + 7 = 15 mph.
   Let t represent the number of hours they are on their bicycles.
   15 5
   5
   15
   1
   3

t

t

t

=

=

=

The girls will meet in^13 of an hour or 20 minutes.

PRACTICE

1. Jessie leaves her house on bicycle, traveling at 8 mph. She is going to