need some help with explanation please!

QUESTION 11 The average spending at Neco's salad bar is $9.9 with a standard deviation of $2.68. The distribution follows t-distribution. The management is interested in the middle 90% of the customers (spending wise) as it believes that they represent their true customer base. What will be the difference between the upper and lower spending cut-offs which dene the middle 90% of the customers if the sample contains 41 customers? QUESTION 12 The average spending at Neco's salad bar is $9.7 with a standard deviation of $3.45. The distribution follows Normal distribution. The management is interested in the middle 80% of the customers (spending wise) as it believes that they represent the customer base. What will be the difference between the upper and lower spending cut-offs which dene the middle 80% of the customers? QUESTION 13 The baking time for a cake is uniformly distributed between 16 and 22 minutes. What is the probability that on a given day, the product will take more than 21.2 minutes? QUESTION 14 The weights of the potatoes is your garden is normally distributed. If the middle 95.44% weigh between 4.82 and 9.21 ounces, then what is the standard deviation of the weights? QUESTION 15 The weights of the tomatoes is normally distributed. If the middle 83% weigh between 2.24 ounces and 5.29 ounces, then what is the mean weight of the tomatos? QUESTION 7 Suppose the probability of someone wearing a pair of glasses among 5th graders is 33.7%. If there are 44 kids in a class, what will be the standard deviation of this distribution? QUESTION 8 Suppose the probability of someone wearing a pair of glasses among 5th graders is 21%. If there are 58 kids in a class, how many of them are expected to have glasses? QUESTION 9 The assembly time for a product is uniformly distributed between 6 and 10 minutes. What is the probability that on a given day, the product will take between 7.2 and 7.9 minutes? QUESTION 10 The average spending at Neco's salad bar is $9.53 with a standard deviation of $3.24. The distribution follows Normal distribution. The management is interested in the middle 85% of the customers (spending wise) as it believes that they represent the customer base. What will be the difference between the upper and lower spending cut-offs which dene the middle 85% of the customers? QUESTION 2 Avisit to a hospital emergency room for something as simple as a sore throat could have a mean cost of $322. Assume that this cost is normally distributed with a standard deviation of $83. If you want to be in the bottom 50%, what will be the cut-off dollar amount? QUESTION 3 Avisit to a hospital emergency room for something as simple as a sore throat could have a mean cost of $317. Assume that this cost is normally distributed with a standard deviation of $99. What is the cut-off dollar amount if you want to be in the top 3% of the patients? QUESTION 4 For a standard normal distribution, the probability of obtaining a Z value between -1.9 to 1.7 is