This bag had 35 green, some black and 3 red marbles. Reaching blindfolded, the probability of picking a red is 1/23. How many black marbles are there.
let B = the number of black marbles.
probability of drawing red:
3/(35 + 3 + B) = 1/23
3/(38 +B) = 1/23
69 = 38 + B
B = 31