In a group of 28 pupils, 12 play the flute only. 6 play the piano only.
9 play neither instrument.
A student is selected at random.
What is the probability the student plays both instruments

hello from mrbilldoesmath!

answer:   x (x+6)^2, choice b

discussion:

factor x out of the equation:

x^3 + 12x^2 + 36x = x (x^2 + 12x + 36).

note that 6+6 = 12 and 6*6 = 36 so the above factors into:

x (x+6)^2

which is choice b

you,

mrb

391.6 is the correct answer