SOLUTION: A fire is reported at a chemical plant on the east side of the city. The fire engine travels an average of 38 mile per hour. It takes the engine 15 minutes to get to the chemical

Question 28365: A fire is reported at a chemical plant on the east side of the city. The fire engine travels an average of 38 mile per hour. It takes the engine 15 minutes to get to the chemical plant. How far away is the chemical plant?
A. 7.1 miles
B. 7.4 miles
C. 8.6 miles
D. 9.2 miles
E. 9.5 miles
I need to figure out how to solve this problem step by step please.
Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!
First, any word problem will have quantities expressed in units.
Time, distance, temperature all have their units. A long time ago, in
high school physics, I learned how to cancel units in an equation.
When all done cancelling, you always get minutes = minutes
or feet = feet, etc. Then you know you handled the units correctly.
The last sentence says "how far" You know the answer will have units of distance, and sure enough, the choices are all in "miles".
distance = rate x time
There aren't many formulas you should memorize, but that is one of them.
Now the thing about cancelling units
Let d = the distance to the chemical plant in miles
The average rate is 38 miles/hour
The time to the chemical plant is 15 minutes
the formula
d miles = 38 miles/hour x 15 minutes
There are "miles" on both sides - that's good. but on the right side,
hours and minutes don't cancel
By cancelling I mean minutes / minutes cancel
You've got minutes / hours
The trick is to insert the fraction
1 hour / 60 minutes as a factor on the right side
That doesn't change anything because 1 hour = 60 minutes and thats
the same as 1/1 or 6/6 or a/a they all = 1
So now
d miles = 38 miles/hour x 15 minutes x 1 hour / 60 minutes
This is perfect- the right side has hours/hours and minutes/minutes,
leaving only miles on the right side
miles = miles
so, leaving out the units,
d = 38 x 15 x 1/60
d = 38 / 4
d = 9.5 miles
Once you get this cancelling of units, it's a great check to see if
you've really got the right answer
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