Noise (except hot pixels) tends to be random so if you take multiple shots of the same scene and combine them you effectively reduce the noise. Some cameras work this way with long exposures.
The way to blend them is if you took five images of the same scene, open then as layers in a program. Then set each of the top four layers opacity to 20% and the bottom layer to 100%. This will reduce the noise really nice. If using ten images you would set to 10% opacity. Three images would see the layers set to 33% opacity.