Compare the values of the two quantities in the question and answer. Quantity 1: A bag contains 20 balls which are red, green and blue. Find the number of red balls in the bag, if the probability of picking a blue ball is 2/5 and that of either a red or a blue ball is 3/4. Quantity 2: A bag contains 25 balls which are red, green and blue. The probability of picking a red ball first is 2/5. If the first ball was red and without keeping it back, probability of picking a blue ball is 1/3, find the number of green balls. Correct Answer Quantity 1 = Quantity 2 Solving for Quantity 1: Probability of picking a blue ball = no. of blue balls/20 = 2/5 ⇒ No. of blue balls = 40/5 = 8 Probability of picking either a red or blue ball = (no. of red balls + no. of blue balls) /20 = ¾ ⇒ No. of red balls + no. of blue balls = 15 ⇒ No. of red balls = 15 – 8 = 7 ⇒ Quantity 1 = 7 Solving for Quantity 2: Probability of picking a red ball first = no. of red balls/25 = 2/5 ⇒ No. of red balls = 10 Probability of picking a blue ball without keeping the first ball back = no. of blue balls/24 = 1/3 ⇒ No. of blue balls = 8 ⇒ No. of green balls = 25 – (10 + 8) = 25 – 18 = 7 ⇒ Quantity 2 = 7 ∴ Quantity 1 = Quantity 2