word problem

Question

A race car drove from Los Angeles to New York in 10 hours but drove back in 9 hours. He was going 10mph faster on the way back. How fat was he driving from Los Angeles to New York?

Answer 1

Distance = rate x time

 

R is the rate of speed

 

 

 

LA to NY:  10 * R <--- 10 hours

NY to LA: 9(R+10) <--- 10 mph faster in 9 hours

 

10 R = 9(R+10)

 

10R = 9R + 90

 

10R - 9R = 90

R = 90

 

90 miles per hour from LA to NY, for 10 hours is 900 miles

 

100 miles per hour from NY to LA, for 9 hours is 900 miles

 

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The only problem is that it's about 3000 miles

from LA to NY. It will actually take the race

car driver 30 hours to go across the country

speeding down I-80 at 100 mph.

Answer 2

This problem belongs to the class of UNIFORM MOTION PROBLEMS.

Many, many such are worked and can be found in our Resources/Answers.

We put them there so that students can search, read, study & learn.

Another kind of related problem has to do with rowing upstream and then downstream in different net times due to the effect of a river's current. I call these 'DRT' problems (Distance, Rate, Time).