Question

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:

2 red marbles

Answer 2

Answer:

No. of Red marbles = 5

Step-by-step explanation:

Solve these for Red & Blue in:

R / (R+B) = 1/5 .........(1)     AND

(R+5) / {(R+5)+B} = 1/3 ..........(2)

Solving (1)

> 5R = R+B

> 4R = B ...........(3)

Substituting (3) in (2)

> (R+5) / {(R+5)+4R} = 1/3

> (R+5) / (5R+5) = 1/3

> 3(R+5) = 5R+5

> 3R+15 = 5R+5

> 2R = 10

> R = 10/2

> R = 5

Therefore,

Number of Red marbles are 5.

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