Question 1189340
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A 747 airplane is fully refueled before takeoff. 
The 747 uses approximately 600 gallons of fuel per minute while flying at the speed of 600 mph 
and approximately 500 gallons per minute while flying at the speed of 500 mph. 
The plane flies for 3 hours at the rate of 600 mph and then slows down for the last 2 hours to 500 mph. 
On this entire flight what was the average number of gallons per mile used by the airplane?
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<pre>
    The average number of gallons per mile = {{{total_gallons/total_miles}}} = {{{(3*60*600 + 2*60*500)/(3*600+2*500)}}} = 60 gallons per mile.
</pre>

Solved.



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Let's make some post-solution estimations.


60 &nbsp;gallons of fuel per mile means &nbsp;60,000 &nbsp;gallons per &nbsp;1,000 miles, &nbsp;which is

about &nbsp;4*60,000 &nbsp;liters of fuel per &nbsp;1,000 &nbsp;miles, &nbsp;or about &nbsp;240 &nbsp;metric tons per &nbsp;1,000 &nbsp;miles,

which is, &nbsp;OBVIOUSLY, &nbsp;absolutely unrealistic.



We all know that the airplanes are apparatuses heavier than air, &nbsp;but with such great load 
as &nbsp;240 &nbsp;metric tons of fuel, &nbsp;no one plane could be able takeoff.



It is interesting to compare this figure with what other &nbsp;(professional) &nbsp;sources tell about it.



Internet web-site https://executiveflyers.com/how-much-fuel-does-a-boeing-747-hold/ 

says that &nbsp;B-747 &nbsp;burns approximately &nbsp;5 &nbsp;gallons of fuel per mile.



It also says that the &nbsp;B-747 &nbsp;is actually a very efficient aircraft and beats other modes of transportation by a long way.



So, &nbsp;the input data in this problem &nbsp;OVER-ESTIMATEs &nbsp;the fuel rate/consumption of &nbsp;B-747 &nbsp;in &nbsp;10 &nbsp;(&nbsp;ten, &nbsp;TEN&nbsp;) &nbsp;times &nbsp;(&nbsp;!&nbsp;) &nbsp;(&nbsp;!&nbsp;)



My warm greetings to the composer of this problem &nbsp;(&nbsp;!&nbsp;)