What Formula Makes a deal good?

[Mark Norris]

I'm Pretty new to being an investor and have been studying the numbers game. So this may sounds stupid however I don't get it should be simple right? Whats the simplest  formal or example of a break down oh how the numbers look on a rental for either a signal family or duplex for a Purchase to rent and hold, Like a quick glance to see if the house is worth perusing?