sophieyu0717
Web site W receives orders for its products every day. What is the standard deviation of the numbers of orders that Web Site W received daily for the past 5 days?
(1) The average (arithmetic mean) number of orders that Web Site W received per day for the past 5 days is equal to the greatest of the numbers of orders that Web Site W received daily for the past 5 days.
(2) The range of the numbers of orders that Web Site W received daily for the past 5 days is equal to 0.
First, you need to understand the meaning of standard deviation. Standard deviation measures how far a certain point is from the mean. For example, let's consider the following data :
(1, 2, 3, 4, 5). The the mean of these data equal (1+2+3+4+5)/5 =15/5 = 3. Now, you can see that the largest point 5 and 1 are two points from the mean. 2 and 4 are 1 point from the mean. 3 is zero point from the mean. The range of our example is equal to the large value minus the smallest value (5-1=4)
Now, let's go back to the main question.
1 telling you that the mean is equal to the greatest number in the set ( for example if the mean is 5 then the greatest and also the smallest numbers are 5 too . This means that all of the five days have the same number of orders thus each day is 0 point from the mean. This is sufficient.
2 is talking about the range. It's telling you that the largest number is equal the smallest number. This means that all of the numbers in the five years are equal, thus each and each day is zero point from the mean. This is sufficient too.