My Math Forum lorry journey

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 December 12th, 2016, 11:38 AM #1 Member   Joined: May 2016 From: Ireland Posts: 92 Thanks: 1 lorry journey a Last edited by markosheehan; December 12th, 2016 at 11:41 AM.
 December 13th, 2016, 09:02 PM #2 Senior Member   Joined: Feb 2016 From: Australia Posts: 1,089 Thanks: 366 Math Focus: Yet to find out. Quite a journey indeed. Thanks from topsquark
 December 16th, 2016, 11:09 AM #3 Member   Joined: May 2016 From: Ireland Posts: 92 Thanks: 1 I made the post and then I figured it out, but I didn't know how to delete it, so instead of people working it out I thought I would just edit it and delete the text. Last edited by skipjack; December 16th, 2016 at 01:13 PM.
December 16th, 2016, 12:42 PM   #4
Senior Member

Joined: Feb 2016
From: Australia

Posts: 1,089
Thanks: 366

Math Focus: Yet to find out.
Quote:
 Originally Posted by markosheehan I made the post and then I figured it out, but I didn't know how to delete it, so instead of people working it out I thought I would just edit it and delete the text.
Haha fair enough . After a certain time passes, you can no longer delete or edit your posts, in case you were wondering. But since you were able to edit, I guess you couldn't find the delete button.

Last edited by skipjack; December 16th, 2016 at 01:14 PM.

 December 16th, 2016, 02:05 PM #5 Global Moderator   Joined: Dec 2006 Posts: 16,928 Thanks: 1253 Say the lorry travels for times $t_1$, $t_2$ and $t_3$ at average speeds of v/2, v and v/2 respectively. As $\dfrac{5v}{6} = \dfrac{t_1v/2 + t_2v + t_3v/2}{t_1 + t_2 + t_3}$, $\dfrac56(t_1 + t_2 + t_3) = t_1/2 + t_2 + t_3/2 = \dfrac12(t_1 + t_2 + t_3) + \dfrac12t_2$, and so $t_2 = 2(5/6 - 1/2)(t_1 + t_2 + t_3) = \dfrac23(t_1 + t_2 + t_3)$.

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