Given the Length and Speed of the train and the time takes by the train to passes the bridge or tunnel, the task is to find the length of the bridge.

**Examples:**

Input: length of train = 120 meters, Speed = 30 m/sec, time = 18 sec

Output: length of bridge = 420 meters.

Input: length of train = 130 meters, Speed = 25 m/sec, time = 21 sec

Output: length of bridge = 395 meters.

**Approach:**

Let the length of the bridge be .

As it is known that **Speed = Distance / Time**

Therefore:

Total distance = (length of train + length of bridge)

=> Speed of train = (length of train + x) / Time.

=> x = (Speed of train * time) – Length of train.

**Formula:**

length of bridge = (speed of train * time taken to cross bridge) – length of train.

Below is the implementation of the above approach:

## C++

`// C++ Program to implement above code. ` ` ` `#include <bits/stdc++.h> ` `using` `namespace` `std; ` ` ` `// function to calculate the length of bridge. ` `int` `bridge_length(` `int` `trainLength, ` `int` `Speed, ` `int` `Time) ` `{ ` ` ` `return` `((Time * Speed) - trainLength); ` `} ` ` ` `// Driver Code ` `int` `main() ` `{ ` ` ` `// Assuming the input variables ` ` ` `int` `trainLength = 120; ` ` ` `int` `Speed = 30; ` ` ` `int` `Time = 18; ` ` ` ` ` `cout << ` `"Length of bridge = "` ` ` `<< bridge_length(trainLength, Speed, Time) ` ` ` `<< ` `" meters"` `; ` ` ` ` ` `return` `0; ` `} ` |

## Java

`//Java Program to implement above code. ` ` ` `public` `class` `GFG { ` ` ` ` ` `//function to calculate the length of bridge. ` ` ` `static` `int` `bridge_length(` `int` `trainLength, ` ` ` `int` `Speed, ` `int` `Time) ` ` ` `{ ` ` ` `return` `((Time * Speed) - trainLength); ` ` ` `} ` ` ` ` ` `//Driver Code ` ` ` `public` `static` `void` `main(String[] args) { ` ` ` ` ` `// Assuming the input variables ` ` ` `int` `trainLength = ` `120` `; ` ` ` `int` `Speed = ` `30` `; ` ` ` `int` `Time = ` `18` `; ` ` ` ` ` `System.out.print(` `"Length of bridge = "` `+ ` ` ` `bridge_length(trainLength, Speed,Time) ` ` ` `+` `" meters"` `); ` ` ` `} ` `} ` |

## Python 3

`# Python 3 Program to implement above code. ` ` ` `# function to calculate the length of bridge. ` `def` `bridge_length(trainLength, Speed, Time) : ` ` ` ` ` `return` `((Time ` `*` `Speed) ` `-` `trainLength) ` ` ` `# Driver Code ` `if` `__name__ ` `=` `=` `"__main__"` `: ` ` ` ` ` `# Assuming the input variables ` ` ` `trainLength ` `=` `120` ` ` `Speed ` `=` `30` ` ` `Time ` `=` `18` ` ` ` ` `print` `(` `"Length of bridge = "` `,bridge_length ` ` ` `(trainLength, Speed, Time),` `"meters"` `) ` ` ` `# This code is contributed by ANKITRAI1 ` |

## C#

`// C# Program to implement above code ` `using` `System; ` ` ` `class` `GFG ` `{ ` ` ` `// function to calculate ` `// the length of bridge ` `static` `int` `bridge_length(` `int` `trainLength, ` ` ` `int` `Speed, ` `int` `Time) ` `{ ` ` ` `return` `((Time * Speed) - trainLength); ` `} ` ` ` `// Driver Code ` `static` `void` `Main() ` `{ ` ` ` `// Assuming the input variables ` ` ` `int` `trainLength = 120; ` ` ` `int` `Speed = 30; ` ` ` `int` `Time = 18; ` ` ` ` ` `Console.Write(` `"Length of bridge = "` `+ ` ` ` `bridge_length(trainLength, Speed, Time) + ` ` ` `" meters"` `); ` `} ` `} ` ` ` `// This code is contributed by Raj ` |

## PHP

`<?php ` `// PHP Program to implement ` `// above code ` ` ` `// function to calculate ` `// the length of bridge ` `function` `bridge_length(` `$trainLength` `, ` ` ` `$Speed` `, ` `$Time` `) ` `{ ` ` ` `return` `((` `$Time` `* ` `$Speed` `) - ` ` ` `$trainLength` `); ` `} ` ` ` `// Driver Code ` ` ` `// Assuming the input variables ` `$trainLength` `= 120; ` `$Speed` `= 30; ` `$Time` `= 18; ` ` ` `echo` `"Length of bridge = "` `. ` ` ` `bridge_length(` `$trainLength` `, ` ` ` `$Speed` `, ` `$Time` `). ` ` ` `" meters"` `; ` ` ` `// This code is contributed by Raj ` `?> ` |

**Output:**

Length of bridge = 420 meters

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the **DSA Self Paced Course** at a student-friendly price and become industry ready.