How many peso in 1 us dollar?

It depends on what country you're referring to. A lot of countries use pesos as their currency and each one has a different value versus the US dollar.

In any case exchange rates change every day so any specific answer posted here would be out of date almost immediately. While it's not normal WikiAnswers policy to say "use the internet", that's the best approach in this case. You can check a site such as www.xe.com, CNNMoney, etc. for the latest conversion factors.