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In a 10 km race, A, B and C each run at uniform speed, get the first, second and third position respectively. If A beats B by 1 km and B beats C by 1 km, then, by how much distance A beat C?

Solution

Correct Option: 2

When A finishes the 10 km race, B has completed 9 km (A beats B by 1 km).

When B finishes the 10 km race, C has completed 9 km (B beats C by 1 km).

Since they run at uniform speeds, the speed ratio equals the distance ratio when time is the same.


When A completes 10 km, B completes 9 km in the same time.

Speed ratio of A to B:

A:B=10:9A : B = 10 : 9


When B completes 10 km, C completes 9 km in the same time.

Speed ratio of B to C:

B:C=10:9B : C = 10 : 9


To combine the ratios A:B=10:9A : B = 10 : 9 and B:C=10:9B : C = 10 : 9:

A:B:C=100:90:81A : B : C = 100 : 90 : 81


When A covers 100 units, C covers 81 units.

When A covers 10 km, C covers:

81100×10=8.1\dfrac{81}{100} \times 10 = 8.1 km


Distance by which A beats C:

108.1=1.910 - 8.1 = 1.9 km

Therefore, A beats C by 1.9 km.

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