Question

Two planes just took off from Salt Lake City, UT. The first plane is traveling 3 times as fast as the second plane. After traveling in the same direction for 7.5 hours, they are 1575 miles apart. What is the average speed of each plane? (Hint: Since they are traveling in the same direction, the distance between them will be the difference of their distances.)

Answer 1

The average speed of the first plane is 315 mph and that of the second plane is 105 mph.

Explanation:

Let us assume that the first plane has speed x mph and that of the second plane is y mph.

So, as per given condition x = 3y ......... (1)

Now, given that after traveling in the same direction for 7.5 hours, they are 1575 miles apart.

So, we write the equation as

7.5x - 7.5y = 1575

⇒ x - y = 210 ........ (2)

Now, solving equation (1) and (2) we get, 3y - y = 210

⇒ 2y = 210

⇒ y = 105 mph

So, from equation (1) we get, x = 3y = 315 mph.

So, the average speed of the first plane is 315 mph and that of the second plane is 105 mph. (Answer)