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Question

In a 100 m race A beats B by 10 m. B beats C by 5 m. By how many meters does A beat C?

The correct answer is
14.5 m

100m Race Dynamics

This problem involves calculating relative distances covered by runners in a race based on given margins.

100m Race: A vs B Performance

When runner A completes the 100 m race, runner B is 10 m behind.

  • A covers 100 m.
  • B covers $100 \text{ m} - 10 \text{ m} = 90 \text{ m}$.

This implies the ratio of distances covered by A and B in the same time is $\frac{\text{Distance}_A}{\text{Distance}_B} = \frac{100}{90}$.

100m Race: B vs C Performance

When runner B completes a race (equivalent to 100 m for comparison), runner C is 5 m behind.

  • B covers 100 m.
  • C covers $100 \text{ m} - 5 \text{ m} = 95 \text{ m}$.

This implies the ratio of distances covered by B and C in the same time is $\frac{\text{Distance}_B}{\text{Distance}_C} = \frac{100}{95}$.

100m Race: Calculating A vs C Margin

We need to determine how far C runs when A finishes the 100 m race.

From the A vs B analysis, when A runs 100 m, B runs 90 m.

Now, we use the B vs C ratio to find C's distance when B runs 90 m:

The ratio $\frac{\text{Distance}_C}{\text{Distance}_B} = \frac{95}{100}$.

Therefore, when $\text{Distance}_B = 90 \text{ m}$, the distance C covers is:

$\text{Distance}_C = 90 \text{ m} \times \frac{95}{100}$

$\text{Distance}_C = 90 \times 0.95 = 85.5 \text{ m}$

Final Beat Margin: A vs C

When A completes the 100 m race, C has run 85.5 m.

The distance A beats C by is the difference between the race distance and C's covered distance:

$100 \text{ m} - 85.5 \text{ m} = 14.5 \text{ m}$

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Important Questions from Speed Time & Distance (Notes)

  1. A and B have to travel from place P to place Q following the same route in their respective cars. A drives at $60$ kmph while B drives at $80$ kmph. Find the time taken by B to reach place Q if A takes $12$ hrs.

  2. On a straight road, a bus is $60$ km ahead of a car running in the same direction. After $3$ hours, the car is $90$ km ahead of the bus. If the speed of the bus is $45$ km/h, then what is the speed of the car (in km/h)?

  3. A train running at the speed of $90$ kmph crosses a $250$ m long platform in $26$ seconds. What is the length of the train (in m)?

  4. A car covers 4 successive stretches of 3 km each at speed of 10 kmph, 20 kmph, 30 kmph and 60 kmph respectively. The average speed of the car for the entire journey is:

  5. A car travels a total distance L. It travels half the distance with speed $v_1$ and the other half with speed $v_2$. The average speed of the car is :
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