distance=rate*t

needhelpmom

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Oct 5, 2005
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At a NASCAR race track, the distance per lap is 2 miles. Lou drives his car at a constant rate of 160 miles per hour.

Ralph drives his car at a constant rate of 170 miles per hour. How long will it take before Ralph gains 2 laps in relation to Lou?

do not know how to figure these word problems out and write an equation can you help me
 
See if you can make sense of this.

No of laps = distance/2

Distance = rate * time


No. of laps = rate/2 *time

Equate the number of laps done by Ralph in t hours with the number of laps done by Lou in t hours plus 2.


170/2*t = 160/2*t + 2


Solve for t

85t = 80t + 2

5t = 2

t = 2/5

So it takes 2/5 of an hour.

2/5 *60 = 24 minutes.

Check!

Calculate the number of laps each does in 24minutes.


(170 * 24/60)/ 2 = 34


(160 * 24/60)/2 = 32

Edit: Galactus' approach is better! I'll leave this up as an example of how you can over complicate these thing
 
Since distance equals rate*time, we must find out how long it takes until Ralph has 4 miles (2 laps) on Lou.

We could write this as:

160t+4=170t, solve for t.

Once you find t, check your answer. Multiply it by 160 and 170, respectively, and see if there is a difference of 4 miles.
 
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