A scientist wants to study the average lifespan of a population of 1000 glow worms. He records the lifespan of a random selection of 60 worms and finds that 20 of them live for 10 months, 15 of them live for 10.5 months, and 25 of them live for 11 months. What is the sample mean of the lifespan of the population of glow worms
