Given four integers **a**, **b**, **c** and **d**. The task is to find the number **X** which when added to the numbers **a** and **b** the ratio changes from **a : b** to **c : d**.

**Examples:**

Input:a = 3, b = 6, c = 3, d = 4Output:6

When 6 is added to a and b

a = 3 + 6 = 9

b = 6 + 6 = 12

And, the new ratio will be 9 : 12 = 3 : 4

Input:a = 2, b = 3, c = 4, d = 5Output:2

**Approach:** Old ratio is **a : b** and new ratio is **c : d**. Let the required number be **X**,

So, **(a + X) / (b + X) = c / d**

or, ad + dx = bc + cx

or, x(d – c) = bc – ad

So, **x = (bc – ad) / (d – c)**

Below is the implementation of the above approach:

`// C++ implementation of the approach ` `#include <bits/stdc++.h> ` `using` `namespace` `std; `
` ` `// Function to return the ` `// required number X ` `int` `getX(` `int` `a, ` `int` `b, ` `int` `c, ` `int` `d) `
`{ ` ` ` `int` `X = (b * c - a * d) / (d - c); `
` ` `return` `X; `
`} ` ` ` `// Driver code ` `int` `main() `
`{ ` ` ` `int` `a = 2, b = 3, c = 4, d = 5; `
` ` ` ` `cout << getX(a, b, c, d); `
` ` ` ` `return` `0; `
`} ` |

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`// Java implementation of the approach ` `import` `java.io.*; `
` ` `class` `GFG `
`{ ` ` ` `// Function to return the ` `// required number X ` `static` `int` `getX(` `int` `a, ` `int` `b, ` `int` `c, ` `int` `d) `
`{ ` ` ` `int` `X = (b * c - a * d) / (d - c); `
` ` `return` `X; `
`} ` ` ` `// Driver code ` `public` `static` `void` `main (String[] args) `
`{ ` ` ` ` ` `int` `a = ` `2` `, b = ` `3` `, c = ` `4` `, d = ` `5` `; `
` ` `System.out.println (getX(a, b, c, d)); `
` ` `} ` `} ` ` ` `// The code is contributed by ajit..@23 ` |

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`# Python3 implementation of the approach ` ` ` `# Function to return the ` `# required number X ` `def` `getX(a, b, c, d): `
` ` ` ` `X ` `=` `(b ` `*` `c ` `-` `a ` `*` `d) ` `/` `/` `(d ` `-` `c) `
` ` `return` `X `
` ` `# Driver code ` ` ` `a ` `=` `2`
`b ` `=` `3`
`c ` `=` `4`
`d ` `=` `5`
` ` `print` `(getX(a, b, c, d)) `
` ` `# This code is contributed by mohit kumar 29 ` |

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`// C# implementation of the approach ` `using` `System; `
` ` `class` `GFG `
`{ ` ` ` `// Function to return the ` `// required number X ` `static` `int` `getX(` `int` `a, ` `int` `b, ` `int` `c, ` `int` `d) `
`{ ` ` ` `int` `X = (b * c - a * d) / (d - c); `
` ` `return` `X; `
`} ` ` ` `// Driver code ` `static` `public` `void` `Main () `
`{ ` ` ` `int` `a = 2, b = 3, c = 4, d = 5; `
` ` `Console.Write(getX(a, b, c, d)); `
`} ` `} ` ` ` `// The code is contributed by Tushil. ` |

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**Output:**

2

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