Question

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A bag contains only red and blue marbles. Yasmine takes one marble at random from the bag. The probability that she takes a red marble is 1 in 5. Yasmine returns the marble to the bag and adds five more red marbles to the bag. The probability that she takes one red marble at random is now 1 in 3. How many red marbles were originally in the bag?

Answer 1

Answer:

Step-by-step explanation:

I got the right answer to this, but only through experimentation. Eg 1 4 5; 2, 8, 10; 3, 12, 15; 4, 16, 20;

5, 20, 25; so adding 5 here to the Reds gives me the right fraction.

A bag contains only red and blue marbles.

Yasmine takes one marble at random from the bag.The probability that she takes a red marble is   1/5.

Yasmine returns the marble to the bag and adds five more red marbles to the bag.The probability that she takes one red marble at random is now 1/3.

Answer 2

Answer:

5 red balls

Step-by-step explanation:

Let the number of red marbles and blue marbles be x and y.

(i) Probability of red marble is 1/5:

⇒ (x/x + y) = 1/5

⇒ 5x = x + y

⇒ 4x = y

(ii) She adds 5 more and takes one red in 1/3:

⇒ (x + 5/x + 5 + y) = 1/3

⇒ 3x + 15 = x + 5 + y

⇒ 2x = y - 10

⇒ 2x = 4x - 10

⇒ x = 5

Therefore, there were 5 red balls in the bag.

Hope it helps!