Answer :

[tex]50-40\%\\ x-100\%\\ \\ 50 \cdot 100=40x\\ 40x=5000\\ x=125\\ Answer:Searched\ number\ is\ 125.[/tex]
[tex]40\%x=50\\0,4x=50/:0,4\\x=125[/tex]
Answer: 50 is 40% of 125.

I hope I helped :D