There are 9 books stacked on a shelf. the thickness of each book is either 1 inch or 2 inches. the height of the stack of 9 books is 14 inches. which system of equations can be used to determine x, the number of 1-inch-thick books in the stack, and y, the number of 2-inch-thick books?

a.) x + y = 14 2x + y = 9

b.) x + y = 14 x + 2y = 9

c.) x + y = 9 x + 2y = 14

d.) x + y = 9 2x + y = 14

Now max recorded the heights of 500 male humans. he found that the heights were normally distributed around a mean of 177 centimeters. which statements about max’s data must be true? a) the median of max’s data is 250 b) more than half of the data points max recorded were 177 centimeters. c) a data point chosen at random is as likely to be above the mean as it is to be below the mean. d) every height within three standard deviations of the mean is equally likely to be chosen if a data point is selected at random.