Age at onset of dementia was determined for a sample of adults between the ages

Age at onset of dementia was determined for a sample of adults between the ages of 60 and 75. For 15 subjects, the results were ΣX = 1008, and Σ(X-M)2 = 140.4. Use this information to answer the following:
1 of 2: Based on the data you have and the Normal Curve Tables, what percentage of people might start to show signs of dementia at or before age 62?

2 of 2: A neuropsychologist is interested only in studying the most deviant portion of this population, that is, those individuals who fall within the top 10% and the bottom 10% of the distribution. She must determine the ages that mark these boundaries. What are these ages?