why is the standard deviation of means generally smaller than the standard deviation of the opopulation of individuals

What are the solutions of the system? solve by graphing. y = -x^2 -6x - 7 y = 2

Which inequality is equivalent to -3x < -12? x < 4 , x < -4 , x > 4, x > -4

Data from 2005 for various age groups show that for each $100 increase in the median weekly income for whites, the median weekly income of blacks increases by $105. also, for workers of ages 25 to 54 the median weekly income for whites was $676 and for blacks was $527. (a) let w represent the median weekly income for whites and b the median weekly income for blacks, and write the equation of the line that gives b as a linear function of w. b = (b) when the median weekly income for whites is $760, what does the equation in (a) predict for the median weekly income for blacks?