Read this: In 2013, a study found that mixed breeds live on average 1.2 years longer than pure breeds, and that increasing body-weight was negatively correlated with longevity (i.e. the heavier the dog the shorter its lifespan).

Mutts, dogs that have several breed characteristics, live how much longer than purebred dogs?
What is the answer? (If it cannot be answered, return "unanswerable")
1.2 years