Question 1151526
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12 times faster than the car? or 12 times AS FAST?<br>
They mean different things, and of course the answers will be different....<br>
If the car's speed is x, then "12 times AS FAST AS" the car is 12x.<br>
If the car's speed is x, then "12 times FASTER THAN" the car is x, plus 12 more times x, or x+12x = 13x.<br>
Unfortunately, in everyday usage the two phrases are used to mean the same thing.<br>
Nearly always, when you see the phrase "x times faster than..." the intended meaning is "x times as fast as...".<br>
In this problem, "12 times as fast as" gives a "nice" answer but "12 times faster than" does not.  So we can assume the intended meaning is "12 times as fast as".<br>
So....<br>
Let x be the speed of the car; then the speed of the plane is 12x.<br>
The time to drive 75 miles at x mph is 75/x; the time to fly 2100 miles at 12x mph is 2100/(12x).<br>
The total time is 4 hours:<br>
{{{75/x + 2100/(12x) = 4}}}<br>
Multiply everything by 12x to clear the fractions:<br>
{{{12*75 + 2100 = 4*12x}}}
{{{3000 = 48x}}}<br>
You can finish from there....<br>