In a 500 m race, the ratio of the speeds of two contestants A and B is 3 : 4. A has a start of 140 m. Then, A wins by:60 m40 m20 m10 mNone

To solve this problem, we first need to understand that the ratio of speeds between A and B is 3:4. This means that for every 3 meters that A runs, B runs 4 meters.

Since A has a start of 140 meters, by the time B starts running, A has already covered 140 meters.

Now, let's calculate the distance A will cover by the time B covers 500 meters (the total length of the race).

Since the speed ratio is 3:4, the distance covered by A when B covers 500 meters is 3/4 * 500 = 375 meters.

But remember, A had a head start of 140 meters. So, the total distance covered by A when B finishes the race is 375 + 140 = 515 meters.

This means that even after B has finished the race, A is still running.

The difference in the distance covered by A and B when B finishes the race is 515 - 500 = 15 meters.

So, A wins by 15 meters.

But this option is not available in the choices given. Therefore, the answer is "None".