The reading speed of sixth graders is approximately normal, with a mean speed of 125 words per minute and a standard deviation of 24 words per minute, Round all decimals to 4 places, including the standard deviation for the sampling distribution of the sample mean. a. What is the standard deviation of the sampling distribution of the sample mean for a sample size of 20? (Round to 4 decimal places). b. Suppose we choose a random sample of 20 sixth graders. What is the probability that their mean reading speed will be less than 122 words per minute? (Round to 4 decimal places). b, Suppose we choose a random sample of 50 sixth graders. What is the probability that their mean reading speed will be less than 122 words per minute? (Round to 4 decimal places)