A train crosses a post in 15 seconds and a platform 100m long in 25seconds. Its length is?Options150 m400 m180 m300 m

To solve this problem, we first need to understand that when a train crosses a post, the distance covered is equal to the length of the train. When a train crosses a platform, the distance covered is equal to the length of the train plus the length of the platform.

1. From the problem, we know that the train crosses a post (i.e., its own length) in 15 seconds. But we don't know the speed of the train yet.

2. We also know that the train crosses a 100m platform in 25 seconds. This means the train plus the platform's length is covered in 25 seconds.

3. Since the speed of the train is constant, we can set up the following equation: (Length of train)/15 seconds = (Length of train + 100m)/25 seconds.

4. Solving this equation will give us the length of the train.

Let's denote the length of the train as 'L'.

So, L/15 = (L + 100)/25.

To solve for L, we first multiply through by 15*25 to get rid of the denominators:

25L = 15L + 1500.

Then, we subtract 15L from both sides to isolate L on one side of the equation:

25L - 15L = 1500,

10L = 1500.

Finally, we divide both sides by 10 to solve for L:

L = 1500 / 10,

L = 150 meters.

So, the length of the train is 150 meters. The correct option is 150 m.