well first add up all the numbers of marbles (which is 34 in total) and divide it by the number of black marbles. (which should give you 8/34) Then simplify the fraction and you should get 4/17
8+14+12= 34 chance of picking a black marble is 8/34 because there are 8 black marbles and 34 marbles in all. the answer reduced is 4/17 because 8/34 ÷2 ( both numerator and denominator are divisible by this number)
