SOLUTION: If a plane flies from Chicago to St. Louis (which is 280 air miles) in 70 minutes, how fast is the plane flying? How do I solve this?

Question 546051: If a plane flies from Chicago to St. Louis (which is 280 air miles) in 70 minutes, how fast is the plane flying? How do I solve this?
Answer by bucky(2189) (Show Source): You can put this solution on YOUR website!
You are looking for the speed (or rate). Use the equation that says:
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Substitute D for distance, R for rate, and T for time to get:
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Does this equation make sense? Sure it does. Suppose your rate or speed while driving a car is 60 miles per hour, meaning that every hour you drive you go 60 more miles. If the time (T) that you spent driving was 3 hours, then the distance you drove is 60 * 3 = 180 miles and that's what the equation tells you to do ... multiply your speed times your driving time to get the distance you went.
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Now let's apply this formula to the problem that you were given. The plane flew a distance (D) of 280 miles. The time it took (T) was 70 minutes. Substitute these two values into this formula and you have:
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Solve for the speed R by dividing both sides by 70 to get:
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Do the division on the left side and the answer becomes:
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So the speed R is 4. What are the units of this speed? Well, the 280 is in units of miles and the 70 is in units of minutes. Therefore, the speed or rate is in units of miles per minute.
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The plane is flying at a rate of 4 miles per minute. Every minute that passes, the plane goes another 4 miles. So in 60 minutes (one hour) at the speed of 4 miles per minute, the plane goes 4 times 60 or 240 miles. Therefore, its speed in miles per hour (a more common unit for airplane speed than miles per minute) is 240 miles per hour.
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Since the problem didn't ask you for any particular units for the speed, you could answer 4 miles per minute or 240 miles per hour. Either answer is correct.
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Hope this helps you to think your way through this problem and understand it. Remember the equation . It is useful in many problems involving speed, distance, and time.
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