Is it legal to promise cash/prize in an application?

Is it legal to promise cash/prize in an application for Google Play.

For example; if i say this in the description of the app, “I’ll give 500$ for the first person who finishes this game.” Is this against the rules?

its probably ok, i guess taxes would be most annoying part of this scheme.

nice idea but u better make this game difficult as hell

Well, yes its okay to promise cash/prize money over the app but one more thing I would say that would not only for the showcasing you have to give out cash/prize otherwise its going to decrease your reputation and yes like @Jaroslaw said better would be making it difficult as hell.

I don’t think it’s legal. The Play store developer terms say no apps for gambling for money or prizes worth money, including games of skill.

But still I can see a number of apps available over the store that offers some prizes like Poker and Rummy gaming apps available over the Google PlayStore.

Its O.k if your offer Cash Promises and prizes to users. Because applications are used by different brands and companies which offers such kinds of attractive companions to get more users. You can use it.