Final answer:
To find the proportion of elementary school children getting between 9 and 10 hours of sleep, calculate the z-scores for 9 and 10 hours and subtract the lower proportion from the higher proportion obtained from the standard normal distribution table or through a calculator.
Step-by-step explanation:
The question revolves around the normal distribution and finding the proportion of a given population within a certain range. To determine the proportion of elementary school children who get between 9 and 10 hours of sleep per night, we will use the z-score formula. The z-score is calculated by subtracting the population mean from the score and then dividing by the standard deviation.
The z-score for 9 hours is (9 - 9.5) / 0.55 = -0.9091. The z-score for 10 hours is (10 - 9.5) / 0.55 = 0.9091. We then look up these z-scores on the standard normal distribution table or use a calculator to find the proportions corresponding to these z-scores. The final proportion is the difference between the proportions for the two z-scores.