A researcher has a colony of Bungo spiders in his lab.

Question

There are 1200 adult spiders in the colony, and the weights are normally distributed with a mean of 11 g and standard deviation of 2 g. Using the 68-95-99.7 rule, about what percent of spiders in the colony way less than 9 g?

Answer 1

9 is 1 standard deviation below the mean of 11. You want to find the percentage of data less than 1 standard deviation below the mean. Per the 68-95-99.7 rule 15.9% of the data is less than 1 standard deviation below the mean.