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A train leaves the station at 6:00pm traveling west at 80 mi/h. On a
parallel track, a second train leaves the station 3 hours later traveling
west at 100 mi/h. At what time will the second train catch up with the
first?
                      Rate            Time              Distance
                      In miles/hour   in hours           in miles

    Train 1                   80            t                 80t

    Train 2
                              100            t-3           100 (t – 3)

      80t = 100( t – 3)
                80t = 100t – 300
                -100t -100t             The first train left at 6:00 pm and 15
                                        hours later the second train caught
               -20t = - 300             up at 9:00 am.
               -20     -20

               t = 15 hours
It takes 1 hour longer to fly to St. Paul at 200 mi/h than it does to return
250 mi/h. How far away is St. Paul?


                     Rate                 Time                   Distance
                     in miles/hour        in hours               In miles

 Going there                 200                 t+1                    200(t + 1)

 Returning                   250                  t                       250t



200(t + 1) = 250t                                200( 4 + 1) =
                                                 200(5) = 1000 miles
         200t + 200 = 250t
         -200t       -200t                       OR 250(4) = 1000 miles

                200 = 50t                        St. Paul is 1,000 miles away.
                 50   50

                    t = 4 hours
On his way to work from home, your uncle averaged only 20 miles per hour.
On his drive home, he averaged 40 miles per hour. If the total travel time was
             1.5 hours, how long did it take him to drive to work?

                       Rate               Time                   Distance


 Home to work                 20                   t                        20t

 Work to home                 40                 1.5 - t                  40( 1.5 – t)


  20t = 40( 1.5 – t)

  20t = 60 – 40t
  +40t      +40t                   It took him 1 hour to drive to work.

  60t = 60

  t = 1 hours
Jane and Peter leave their home traveling in opposite directions on a straight
road. Peter drives 15 mi/h faster then Jane. After 3 hours, they are 225 miles
                   apart. Find Peter’s rate and Jane’s rate.

                       Rate                     Time                Distance

Jane
                                      r                3                       3r

Peter                                                                     3( r + 15)
                                 r + 15                3


   3r + 3( r + 15) = 225

             3r + 3r + 45 = 225
                                                 Jane was driving 30 miles/hour and
                  6r + 45 = 225                  Peter was driving 45 miles/hour.
                      -45 -45

                           6r = 180

                            r = 30 miles/hour
Sarah and John Leave Perryville traveling in opposite directions on a straight
road. Sarah drives 12 miles per hour faster than John. After 2 hours, they are
               176 miles apart. Find Sarah and John’s speeds.

                       Rate              Time                  Distance

Sarah                         r + 12              2                 2( r +12)

John
                                 r                2                    2r


2(r+12) + 2r = 176

2r + 24 + 2r = 176
                                       John’s speed is 38 mils per hour and Sarah’s
       4r + 24 = 176                   is 50 miles per hour.
           -24 -24

            4r = 152

             r = 38 miles/hour
In general…
• Define your variable to represent your
  unknown and use this to define other
  quantities
• There are 3 kinds of r(t)=d problems
  – Same direction
  – Opposite Direction
  – Round trip
The width of a rectangle is 3 inches less than its length. The perimeter is 26
                inches. What is the width of the rectangle?




                                                                       L-3




                                      L

Let L = length and Let W = L- 3           Perimeter = 2L + 2W

                              26 = 2L + 2( L - 3)
                              26 = 2L + 2L -6
                              26 = 4L - 6                  So the width of the
                              +6      +6                   rectangle is 5 inches long.

                              32 = 4L
                               4 4
                              L = 8 inches
The sum of 3 even consecutive numbers is 66. Find the 3 numbers.


Let n = the first number

Let n + 2 = the second number                       20, 22, 24
Let n + 4 = the third number

                           n + n + 2 + n + 4 = 66
                                     3n + 6 = 66
                                         -6 -6

                                         3n = 60
                                         n = 20

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3.6 lesson (word problems)

  • 1. A train leaves the station at 6:00pm traveling west at 80 mi/h. On a parallel track, a second train leaves the station 3 hours later traveling west at 100 mi/h. At what time will the second train catch up with the first? Rate Time Distance In miles/hour in hours in miles Train 1 80 t 80t Train 2 100 t-3 100 (t – 3) 80t = 100( t – 3) 80t = 100t – 300 -100t -100t The first train left at 6:00 pm and 15 hours later the second train caught -20t = - 300 up at 9:00 am. -20 -20 t = 15 hours
  • 2. It takes 1 hour longer to fly to St. Paul at 200 mi/h than it does to return 250 mi/h. How far away is St. Paul? Rate Time Distance in miles/hour in hours In miles Going there 200 t+1 200(t + 1) Returning 250 t 250t 200(t + 1) = 250t 200( 4 + 1) = 200(5) = 1000 miles 200t + 200 = 250t -200t -200t OR 250(4) = 1000 miles 200 = 50t St. Paul is 1,000 miles away. 50 50 t = 4 hours
  • 3. On his way to work from home, your uncle averaged only 20 miles per hour. On his drive home, he averaged 40 miles per hour. If the total travel time was 1.5 hours, how long did it take him to drive to work? Rate Time Distance Home to work 20 t 20t Work to home 40 1.5 - t 40( 1.5 – t) 20t = 40( 1.5 – t) 20t = 60 – 40t +40t +40t It took him 1 hour to drive to work. 60t = 60 t = 1 hours
  • 4. Jane and Peter leave their home traveling in opposite directions on a straight road. Peter drives 15 mi/h faster then Jane. After 3 hours, they are 225 miles apart. Find Peter’s rate and Jane’s rate. Rate Time Distance Jane r 3 3r Peter 3( r + 15) r + 15 3 3r + 3( r + 15) = 225 3r + 3r + 45 = 225 Jane was driving 30 miles/hour and 6r + 45 = 225 Peter was driving 45 miles/hour. -45 -45 6r = 180 r = 30 miles/hour
  • 5. Sarah and John Leave Perryville traveling in opposite directions on a straight road. Sarah drives 12 miles per hour faster than John. After 2 hours, they are 176 miles apart. Find Sarah and John’s speeds. Rate Time Distance Sarah r + 12 2 2( r +12) John r 2 2r 2(r+12) + 2r = 176 2r + 24 + 2r = 176 John’s speed is 38 mils per hour and Sarah’s 4r + 24 = 176 is 50 miles per hour. -24 -24 4r = 152 r = 38 miles/hour
  • 6. In general… • Define your variable to represent your unknown and use this to define other quantities • There are 3 kinds of r(t)=d problems – Same direction – Opposite Direction – Round trip
  • 7. The width of a rectangle is 3 inches less than its length. The perimeter is 26 inches. What is the width of the rectangle? L-3 L Let L = length and Let W = L- 3 Perimeter = 2L + 2W 26 = 2L + 2( L - 3) 26 = 2L + 2L -6 26 = 4L - 6 So the width of the +6 +6 rectangle is 5 inches long. 32 = 4L 4 4 L = 8 inches
  • 8. The sum of 3 even consecutive numbers is 66. Find the 3 numbers. Let n = the first number Let n + 2 = the second number 20, 22, 24 Let n + 4 = the third number n + n + 2 + n + 4 = 66 3n + 6 = 66 -6 -6 3n = 60 n = 20