I have some mangoes lying around the house that I am curious to use in a banana bread.
Suppose I puree the mangoes and I have one banana. How much mango puree should I use to make a mango-banana bread?
Mango puree is quite a bit more acidic than banana; 3.4 to 4.6. vs about 6.5. Quite a bit more liquid too. I'd cut to about two bananas worth volume wise, and be quick about stirring in the puree and getting it into your oven. The low pH is liable to set off your rising agent quickly. Take it too slow, and you'll have bread overfilling the pan, or flatbread.
My banana bread/cake calls for 2 cups of mashed bananas. I use 1 cup mashed ripe bananas (the riper the sweeter) and 1 cup mango puree (strained to remove strings). It comes out very moist.