Respuesta :

mudinprincess
8+8=16
16-1=15
7+8=15

not sure if this is wha your talking about but this is how I was taught good luck :)
mrkmusvovzdeq

Based on research, a double fact is "1 + 1" or "2 + 2"

I don't really know what you mean about 7 + 8 being a double fact.