A train passes two bridges of lengths 500m and 250m in 100 seconds and 60 seconds respectively. The length of the train isa.250mb.125mc.120md.152m

To solve this problem, we need to understand that when a train crosses a bridge, it covers the distance equal to the length of the train plus the length of the bridge.

1. Let's denote the length of the train as 'x'. So, when the train crosses the first bridge, it covers a distance of x + 500m in 100 seconds. Therefore, the speed of the train is (x + 500) / 100.

2. Similarly, when the train crosses the second bridge, it covers a distance of x + 250m in 60 seconds. Therefore, the speed of the train is (x + 250) / 60.

3. Since the speed of the train remains constant, we can equate the two expressions we got for the speed and solve for 'x':

   (x + 500) / 100 = (x + 250) / 60

4. Cross-multiplying gives us 60x + 30000 = 100x + 25000

5. Simplifying this gives us 40x = 5000

6. Solving for 'x' gives us x = 5000 / 40 = 125m

So, the length of the train is 125m. Therefore, the correct answer is (b) 125m.