The equation would be 28/3 because there are 28 students in the class and the ratio of boystogirlsis 3-9 meaning that it is 1/3, which is the same as dividing by 3, so the equation would be 28/3
Students with D's / total students : 3 / (7 + 9 + 11 + 3 + 2) = 3 / 32 = 0.0937...to turn to a percent, multiply by 100 = 9.375....rounded = 9.4% <== ur probability