How many 18" square tiles are needed to pave the door of a patio that measures
18 by 15

assuming you want to cover 18 ft x 15 ft:

18 x 15 = 270 ft²

1.5 x 1.5 = 2.25 ft² per tile

270 ft²/ 2.25 per tile = 120 tiles

an advantage of the standard deviation is that it increases as the dispersion of the data increases. e. the interquartile range is preferred when the data are not skewed or no have outliers. an advantage of the standard deviation is that it uses all the observations in its computation.