Element X is a radioactive isotope such that every 81 years, its mass decreases by half. Given that the initial mass of a sample
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Answer:
30 mph
Step-by-step explanation:
Let d = distance (in miles)
Let t = time (in hours)
Let v = average speed driving <u>to</u> the airport (in mph)
⇒ v + 15 = average speed driving <u>from</u> the airport (in mph)
Using: distance = speed x time
Create two equations for the journey to and from the airport, given that the distance one way is 18 miles:
We are told that the total driving time is 1 hour, so the sum of these expressions equals 1 hour:
Now all we have to do is solve the equation for v:
As v is positive, v = 30 only
So the average speed driving to the airport was 30 mph
(and the average speed driving from the airport was 45 mph)