January 24th, 2012, 03:25 AM  #1 
Member Joined: Jan 2012 Posts: 33 Thanks: 0  Text exercise
At a highschool crosscountry meet, Jared jogged 8 mph for the first part of the race, then increased his speed to 12 mph for the second part. If the race was 21 mi long and Jared finished in 2 hr, how far did he jog at the faster pace? 
January 24th, 2012, 03:37 AM  #2 
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,958 Thanks: 1146 Math Focus: Elementary mathematics and beyond  Re: Text exercise
Let x be how long Jared ran at 8 mph and y be how long Jared ran at 12 mph. Distance equals speed multiplied by time: 8x + 12y = 21 Total time for the trip was 2 hours, so we have the system 8x + 12y = 21 x + y = 2. Can you work with that? 
January 24th, 2012, 03:40 AM  #3 
Newbie Joined: Oct 2011 From: Turkey Posts: 29 Thanks: 0  Re: Text exercise
8(2x)+12x=21 168x+12x=21 x=1,25 21,25=0,75 1,25*12=15 0,75*8=6 15+6=21 
January 24th, 2012, 04:11 AM  #4 
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,958 Thanks: 1146 Math Focus: Elementary mathematics and beyond  Re: Text exercise
The correct answer is 15 miles.

January 24th, 2012, 04:28 AM  #5 
Member Joined: Jan 2012 Posts: 33 Thanks: 0  Re: Text exercise
Jeff had a job interview in a nearby city 72 mi away. On the first leg of the trip he drove an average of 30 mph through a long construction zone, but was able to drive 60 mph after passing through this zone. If driving time for the trip was 1 1/2 hr, how long was he driving in the construction zone? I got answer 36min, correct ? 
January 24th, 2012, 04:45 AM  #6 
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,958 Thanks: 1146 Math Focus: Elementary mathematics and beyond  Re: Text exercise
Yes, that is correct.

January 24th, 2012, 04:51 AM  #7 
Member Joined: Jan 2012 Posts: 33 Thanks: 0  Re: Text exercise
30(1.5t) + 60t = 72 45  30t + 60t = 72 30t = 27 t = 0.9 1.5  0.9 = 0.6 60 * 0.6 = 36 this is correct ? 
January 24th, 2012, 04:55 AM  #8 
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,958 Thanks: 1146 Math Focus: Elementary mathematics and beyond  Re: Text exercise
Yes; good work.

January 24th, 2012, 05:10 AM  #9 
Member Joined: Jan 2012 Posts: 33 Thanks: 0  Re: Text exercise
But it says how long was he driving in the construction zone? So I would need to find how long he drove when his speed was 30mph ? 60t + 30t = 72 t = 0.8 * 1.5 = 1.2 30 * 1.2 = 36 too So which one ? I'm mixed up 
January 24th, 2012, 05:17 AM  #10  
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,958 Thanks: 1146 Math Focus: Elementary mathematics and beyond  Re: Text exercise Quote:
0.6 x 60 = 36 minutes, and that is the correct answer. To avoid confusion, choose the method you are most comfortable with and work with that.  

Tags 
exercise, text 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Needs help with this text book question  roberto.salamanca  Algebra  8  January 31st, 2014 10:45 AM 
A challenging text for me.  goedelite  Real Analysis  1  September 7th, 2012 03:58 PM 
A good PDE text  abcdefgh  Math Books  0  June 5th, 2012 06:36 AM 
Looking for a more rigorous text  shaunak84  Math Books  2  February 28th, 2012 08:07 PM 
Text exercise  thinkfast  Algebra  8  January 21st, 2012 12:01 AM 