Math Problem Statement
Two boats go downstream from A to B. The faster boat covers the distance from A to B, 1.5 times as fast as the slower boat. It is known that for every hour the slower boat
lags behind the faster boat by 8 km. However, if they go upstream, then the faster boat covers the distance B to A in half the time as the slower boat. Find the speed of the
faster boat in still water.
A. 12 k/h
B. 20 k/h
C. 24k/h
D. 25k/h
Solution
Let the speed of the faster boat in still water be , and let the speed of the slower boat in still water be . The speed of the current is .
Downstream Scenario:
- When the boats go downstream (with the current), their effective speeds are:
- Faster boat:
- Slower boat:
We are given that the faster boat covers the distance from A to B times as fast as the slower boat, which means the time taken by the faster boat is of the time taken by the slower boat.
Let the distance from A to B be . Then, using the formula for time , we have:
Simplifying this equation:
Also, it is given that for every hour, the slower boat lags behind the faster boat by . This means:
Upstream Scenario:
- When the boats go upstream (against the current), their effective speeds are:
- Faster boat:
- Slower boat:
We are given that the faster boat covers the distance from B to A in half the time taken by the slower boat. So:
Simplifying this:
Solving the System of Equations:
We now have the system of three equations:
Substitute from Equation 3 into Equation 1:
So, .
Now, substitute into Equation 3:
Finally, substitute into Equation 2:
Now, substitute into :
Answer:
The speed of the faster boat in still water is . Therefore, the correct option is:
Would you like a detailed explanation of any part, or have further questions?
Here are 5 related questions you might find useful:
- What is the formula for effective speed when moving with or against the current?
- How do you set up equations for relative speeds of two moving objects?
- How does the current's speed affect the overall travel time?
- How can you solve linear equations involving two variables?
- What are some other examples of word problems involving boats and currents?
Tip: When solving word problems, carefully translate the problem into mathematical equations before attempting to solve them!
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Math Problem Analysis
Mathematical Concepts
Algebra
System of Linear Equations
Relative Speed
Boats and Currents
Formulas
Time = Distance / Speed
Relative Speed Downstream: Speed with current = Speed in still water + Speed of current
Relative Speed Upstream: Speed against current = Speed in still water - Speed of current
Theorems
Linear Equations
Suitable Grade Level
Grades 9-12
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