Answer and Explanation
Your Answer is
Correct Answer is B
Explanation
Assume the desired value is x, so (8+x)/(20+x)=2/5, x=10, choose B
25. A bag contains 8 red marbles, 5 yellow marbles, and 7 green marbles.How many additional red marbles must be added to the 20 marbles already in the bag so that the probability of randomly drawing a red marble is 
？