Two fractions with different denominators that have the sum of 1/3

What is the standard deviation of the following data set rounded to the nearest tenth? 3, 17, 18, 15, 12, 21, 9

Which of the following equations is of the parabola whose vertex is at (4, 3), axis of symmetry parallel to the y-axis and focus at (4, -3)? a.) y+3=1/24 (x+4)^2 b.)y-3=-1/24 (x-4)^2 c.)x-4=-1/24 (y-3)^2

Which value of m will create a system of parallel lines with no solution? y= mx - 6 8x - 4y = 12