Math Problem Statement
A train leaves station A at 5:00 am and reaches station B at 9:00 am on the same day. Another train leaves station B at 7:00 am and reaches station A at 10:30 am on the same day. The time at which the two trains cross one another is
A. 8:00 am
B. 8:26 am
C. 7:26 am
D. 7:56 am
Solution
To solve this problem, we first need to calculate the speeds of the two trains and then determine the time they meet. Let the distance between Station A and Station B be (in kilometers). Here’s the step-by-step process:
Step 1: Calculate the speed of the first train
The first train travels from A to B in 4 hours (from 5:00 am to 9:00 am). Its speed is:
Step 2: Calculate the speed of the second train
The second train travels from B to A in hours (from 7:00 am to 10:30 am). Its speed is:
Step 3: Write the relative positions as functions of time
Let represent the time (in hours) after 7:00 am when the two trains meet. At this moment:
- The first train has already been traveling for hours (it started at 5:00 am).
- The second train has been traveling for hours (it started at 7:00 am).
The distance covered by the first train is:
The distance covered by the second train is:
Since the two trains meet, the sum of these distances equals :
Step 4: Solve the equation
Substitute the expressions for and :
Divide through by (since ):
Eliminate the fractions by multiplying through by 28 (the least common multiple of 4 and 7):
Simplify:
Combine terms:
Solve for :
Step 5: Convert to minutes
Thus, the two trains meet approximately after 7:00 am. This is around 7:37 am.
Correct Answer:
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Math Problem Analysis
Mathematical Concepts
Speed and Time
Relative Motion
Algebra
Formulas
Speed = Distance / Time
Relative Motion: Distance1 + Distance2 = Total Distance
Theorems
Relative Motion Theorem
Linear Equation Solving
Suitable Grade Level
Grades 9-11
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