I have a hard time finding the the key that a song is in, so I tried something different. While the song is playing a I played a pentatonic scale in different keys until I found one that sounded right. It seems to work, but I'm curious if others find this to be an easy way to find the key ? Thanks
The two missing notes from a full diatonic major scale to a pent. major are the two which are important in the V7 chord. So when the song is at that V7 chord, the pent. notes won't be a good fit to anything. So, to me it's a bit of a red herring. Also, there are the major and minor pents, which could prove to be misleading.
However, if it works for you, well and good. For me, just listening to the bass line, and getting to a cadence that feels it's come home is enough - more often than not, it's a perfect cadence (V>I) and that gives the I point where the root of the key will be obvious.
If all else fails, assuming there's no key change or modulation, the last chord will 99% of the time be the key chord - providing, of course, that the song doesn't fade out...