Chunli M. answered • 08/14/16
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the trip is 5 hours, we assume that
the first part it takes x hours at speed 105 mph,
the second part it takes y hours at speed 115 mph.
x + y = 5 that is x = 5- y this is equation 1
105 x + 115 y = 555 this is equation 2
put equation 1 into equation 2, we get
105(5 - y) + 115 y = 555
525 -105 y+ 115 y = 555
y = 3
then x = 5 - y =5 - 3 = 2
so 105 x= 105 * 2 = 210
115 y= 115 *3 = 345
the plan fly 210 mile at speed 105 mph,
the plan fly 345 mile at speed 115 mph.
Chunli M.
When I answer the question, I assume the time the plane takes at each speed with x and y, and then get the value of x and y, that is, we obtain how long the plane takes at each speed.
Then I give the distance the plane traveled at each speed, I answered the question much more.
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08/15/16
Mark M.
No matter how elegant - or elaborate - the algebraic solution, it is worthless unless it answers the verbal question. This must be the case is physics as well. It is a condition that is always taught in secondary Algebra classes.
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08/15/16
Chunli M.
you don't think I answered the time it takes at each speed?
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08/15/16
Mark M.
The last two lines state distance and speed. Nothing is mentioned as to time.
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08/15/16
Chunli M.
that two sentence I answered too more, did you see the value of x and y?
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08/15/16
Mark M.
Yes, I had to reread you solution to locate it and use it to answer the question.
The question of the problem is: For how long did the plan (six) fly at each speed. Appropriately, the answer would be:
At 105mph the plan flew for two hours, then at 115mph the plane flew three hours.
These questions probably come from students in a secondary class in which a word problem can be "discounted" if the appropriate answer is not given. Consider that.
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08/15/16
Mark M.
08/14/16