In other words, households that fall at the 90th percentile for wealth have about 115 times as much wealth as households at the 25th percentile. We know from Figure 6.18 that the distribution of household wealth in the United States is extremely skewed to the right. However, imagine that we asked American adults to estimate the ratio of the 90th to the 25th percentile for household wealth. Imagine that these estimates were normally distributed, as shown in Figure 6.19.

a. The mean of the distribution in Figure 6.19 is 75, and the standard deviation is