Answered

Two cars that are 150 miles apart start driving toward each other on parallel roads. The average speed of the first car is 60 miles per hour. The average speed of the second car is 55 miles per hour. Which equation can be used to determine $t$, the time it takes for the two cars to pass each other?




Rate (mi/h)Time (h)Distance (miles)

First Car
60$t$60t

Second Car
55$t$$55 t$





A$60 t-55 t=0$
B$60 t+55 t=1$
C$60 t+55 t=150$
D$60 t-55 t=150$

Verified Answer :

  • Express the distance traveled by each car using the formula \(\text{distance} = \text{rate} \times \text{time}\).
  • Note that the first car travels \(60t\) miles and the second travels \(55t\) miles.
  • Since the cars move toward each other and meet at a total distance of \(150\) miles, equate the sum of their individual distances to the total initial distance.
  • The resulting equation is \(\boxed{60t + 55t = 150}\).

Explanation

  1. Analyzing the Given Information

Two cars start at an initial distance of \(150\) miles from each other and travel toward one another. Let \(t\) represent the time in hours it takes for the two cars to pass each other. We are given the following information:

  • The speed of the first car is \(60\) miles per hour.
  • The speed of the second car is \(55\) miles per hour.
  • The time each car travels before meeting is \(t\).

Since distance is the product of rate and time (\(d = r \times t\)), the distance traveled by the first car is \(60 \times t = 60t\) miles, and the distance traveled by the second car is \(55 \times t = 55t\) miles.

  1. Formulating the Equation

When the two cars pass each other, they will have covered a total combined distance equal to their initial starting distance. This is because they start at two different locations and move toward each other until their paths intersect. Thus, the sum of the distances traveled by both cars must equal the initial gap between them:
\[\text{Total distance} = \text{Distance of first car} + \text{Distance of second car}\]
Substituting the expressions derived in the previous step:
\[150 = 60t + 55t\]
Alternatively written as:
\[60t + 55t = 150\]
This equation allows us to solve for the time \(t\).

  1. Concluding the Answer

Comparing the derived equation \(60t + 55t = 150\) with the given options:

  • \(60t - 55t = 0\)
  • \(60t + 55t = 1\)
  • \(60t + 55t = 150\)
  • \(60t - 55t = 150\)

The third option matches our derived equation perfectly. Therefore, the equation to determine the time \(t\) is \(60t + 55t = 150\). The final answer is \(\boxed{60t + 55t = 150}\).

Examples

This problem is a classic example of relative motion. Similar principles are used by air traffic controllers or logistics managers to calculate arrival times, ensure safety, and coordinate movements of multiple objects or vehicles. For example, if two trains are on parallel tracks headed toward each other, knowing their speeds and the track distance allows you to predict exactly when they will cross paths, which is essential for scheduling and safety.