SOLUTION: This question is not from a book. Steve traveled 150 miles at a certain speed. Had he gone 20mph faster the trip would have taken 2 hours less. Find the speed of his vehicle

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Question 186871: This question is not from a book.
Steve traveled 150 miles at a certain speed. Had he gone 20mph faster the trip would have taken 2 hours less. Find the speed of his vehicle

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let r= the speed of the vehicle
Let d= distance in miles
Let t = time in hours
given:
d+=+150 mi
d+=+r%2At
(1) 150+=+r%2At
(2) 150+=+%28r+%2B+20%29%2A%28t+-+2%29
---------------------------------
From (1),
t+=+150%2Fr
Substitute this in (2)
(2) 150+=+%28r+%2B+20%29%2A%28%28150%2Fr%29+-+2%29
(2) 150+=+150+%2B+3000%2Fr+-+2r+-+40
Subtract 150 from both sides
(2) 0+=+3000%2Fr+-+2r+-+40
Add 40 to both sides
(2) 40+=+3000%2Fr+-+2r
Multiply both sides by r
(2) 40r+=+3000+-+2r%5E2
Add 2r%5E2 to both sides
(2) 2r%5E2+%2B+40r+=+3000
divide both sides by 2
(2) r%5E2+%2B+20r+=+1500
I will find r by completing the square
(you could use quadratic formula also)
(2) r%5E2+%2B+20r++%2B+%2820%2F2%29%5E2+=+1500+%2B+%2820%2F2%29%5E2
(2) r%5E2+%2B+20r++%2B+100+=+1500+%2B+100
(2) r%5E2+%2B+20r++%2B+100+=+1600
Now both sides are perfect squares
(2) %28r+%2B+10%29%5E2+=+40%5E2
Take the square roots of both sides
(2) r+%2B+10+=+40
(2) r+=+30 (there is a negative solution also, r+=+-50)
The speed of his vehicle is 30 mi/hr
check answer:
(1) 150+=+r%2At
(1) t+=+150%2F30
(1) t+=+5 hrs
and
(2) 150+=+%28r+%2B+20%29%2A%28t+-+2%29
(2) 150+=+%2830+%2B+20%29%2A%285+-+2%29
(2) 150+=+50%2A3
(2) 150+=+150
OK