Math Problem Statement

In a 1000 metres race, A beats B by 200m and B beats C by 200 metres. What is the ratio of the number of seconds by which A beats C to the number of seconds by which A beats B?

Solution

Let's break the problem down step by step.

Information Given:

  • A beats B by 200 meters in a 1000-meter race.
  • B beats C by 200 meters in a 1000-meter race.

This means:

  • When A runs 1000 meters, B runs only 800 meters (since A beats B by 200 meters).
  • Similarly, when B runs 1000 meters, C runs only 800 meters (since B beats C by 200 meters).

Step 1: Find the time taken by A, B, and C to finish the race.

Let’s assume that A, B, and C run the race at constant speeds, and let tAt_A, tBt_B, and tCt_C represent the times taken by A, B, and C to complete the 1000-meter race.

  1. A's speed:
    Speed of A is vA=1000tAv_A = \frac{1000}{t_A}.

  2. B's speed:
    Since B runs 800 meters when A runs 1000 meters, we can express B’s speed relative to A’s speed: vB=8001000vA=0.8vAv_B = \frac{800}{1000} \cdot v_A = 0.8 \cdot v_A The time taken by B to complete 1000 meters is: tB=1000vB=10000.8vA=1250vAt_B = \frac{1000}{v_B} = \frac{1000}{0.8 \cdot v_A} = \frac{1250}{v_A}

  3. C's speed:
    Similarly, C runs 800 meters when B runs 1000 meters, so C’s speed relative to B’s speed is: vC=8001000vB=0.8vB=0.80.8vA=0.64vAv_C = \frac{800}{1000} \cdot v_B = 0.8 \cdot v_B = 0.8 \cdot 0.8 \cdot v_A = 0.64 \cdot v_A The time taken by C to complete 1000 meters is: tC=1000vC=10000.64vA=1562.5vAt_C = \frac{1000}{v_C} = \frac{1000}{0.64 \cdot v_A} = \frac{1562.5}{v_A}

Step 2: Calculate the time differences.

  • Time by which A beats B: Time difference=tBtA=1250vA1000vA=250vA\text{Time difference} = t_B - t_A = \frac{1250}{v_A} - \frac{1000}{v_A} = \frac{250}{v_A}

  • Time by which A beats C: Time difference=tCtA=1562.5vA1000vA=562.5vA\text{Time difference} = t_C - t_A = \frac{1562.5}{v_A} - \frac{1000}{v_A} = \frac{562.5}{v_A}

Step 3: Find the ratio.

Now, we find the ratio of the time by which A beats C to the time by which A beats B: Ratio=562.5vA250vA=562.5250=2.25\text{Ratio} = \frac{\frac{562.5}{v_A}}{\frac{250}{v_A}} = \frac{562.5}{250} = 2.25

Final Answer:

The ratio of the number of seconds by which A beats C to the number of seconds by which A beats B is 2.25.


Would you like further clarification or have any questions?

Here are some related questions for you to consider:

  1. How would the ratio change if A beat B by 100 meters instead of 200 meters?
  2. If the race distance was doubled to 2000 meters, how would the times for A, B, and C change?
  3. How do you calculate the relative speeds in a race where one competitor beats another by a specific distance?
  4. What is the significance of a ratio greater than 1 in a race context?
  5. How can you use the concept of relative speeds to solve similar race problems?

Tip: When working with race problems involving relative distances, it's helpful to express all competitors' speeds in terms of one competitor's speed. This simplifies the calculation of time differences.

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Math Problem Analysis

Mathematical Concepts

Relative Speed
Time Calculation
Ratios

Formulas

Speed = Distance / Time
Time = Distance / Speed
Relative Speed = (Speed of A / Speed of B) when one competitor beats another by a given distance

Theorems

Relative speed in races
Time and distance relationship

Suitable Grade Level

Grades 8-10