Question: There are 4 blue marble labelled P, 7 blue marbles labelled Q, 3 green marbles labelled P, 9 green marbles labelled Q. Two marbles are drawn at random from the box. Find the probability that both the marbles are of the same colour but labelled iwth a different letter.
Why is the answer 4/23 x 7/22 + 3/23 x 9/22 = 5/46 ?
My own answer is :
Probability of (first ball blueP & second ball blueQ, or first ball blueQ & second ball blueP, or first ball greenP & seocnd ball greenQ , or first ball greenQ & second ball greenP ) = 4/23 x 7/22 + 7/23 x 4/22 + 3/23 x 9/22 + 9/23 x 3/22 = 5/23
Why is my answer wrong?
Why is the answer 4/23 x 7/22 + 3/23 x 9/22 = 5/46 ?
My own answer is :
Probability of (first ball blueP & second ball blueQ, or first ball blueQ & second ball blueP, or first ball greenP & seocnd ball greenQ , or first ball greenQ & second ball greenP ) = 4/23 x 7/22 + 7/23 x 4/22 + 3/23 x 9/22 + 9/23 x 3/22 = 5/23
Why is my answer wrong?
