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In a $100$ meters race, $A$ beat $B$ by $10$ meter or $2$ second. What is the speed of $A$?

1. $5$ Km/h
2. $10$ Km/h
3. $15$ Km/h
4. $20$ Km/h

We know both of them covers 100 m, but

t(B) = t(A) +2

For last 10m, B took 2 sec more to cover that distance, hence

Speed of B = 5 m/sec

B covered 100 meters in 20 sec so,

A covered 100 meters in 18 sec

Speed of A = 100/18 * 18/5 = 20 Km/h

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