2-3 How much longer does it take?

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  • #1
karush
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You normally drive on the freeway between San Diego and Los Angel es at an average speed of $105 \, km/h \, (65 \, mi/h)$ and the trip takes $2h$ and $20 \, min$
On a Friday afternoon, however, heavy traffic slows you down and you drive the same distance at an average speed of only
$70 km/h \, (43 mi/h)$
How much longer does it take?
$d_1=r_1t_1=\dfrac{65\,mi}{\cancel{ h }} \cdot 2.33\, \cancel{h}=151.45\,mi$
$t_2=\dfrac{d_1}{r_2}=151.45\,\cancel{mi}\cdot\dfrac{h}{43\,\cancel{mi}}=3.52\,h$
$t_\Delta=t_2-t_1=3.52h-2.33h\approx 1.19\, h \approx 1\, h\, 10\, min$

ok I still get ? with these word problems so...hopefully
 

Answers and Replies

  • #2
Kansas Boy
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Driving at 105 km/hr it takes 2 hours and 20 minutes= 2 and 1/3 hours= 7/3 hours to drive from San Diego to Los Angeles. So how far is it from San Diego to Los Angeles? How long will it take to drive from San Diego to Los Angles at 70 km/h?
 
  • #3
Kansas Boy
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Since this has been here a week now without any more response:

It takes 7/3 hours to drive at 105 km/h between San Diego and Los Angeles so they are (7/3)(105)= 7(35)= 245 km apart.

If, instead, you drive at 70 km/h it will take 245/70= 3.5 hours or 3 hours and 30 minutes. That is one hour and ten minutes longer.
 

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