UCAT Medentry DM Question

Could someone draw this as a probability tree I thought it was just 1/6 because there's 1 black out of 6 but explanation says otherwise..

Reply 1

charlotte05x

Original post by charlotte05x

Could someone draw this as a probability tree I thought it was just 1/6 because there's 1 black out of 6 but explanation says otherwise..

sorry i forgot to attach: Screenshot (464).png

Reply 2

mqb2766

Presuming the answer A is yes, its 1/6. You could get it by drawing a tree as per the reasoning in the model solution or a counting argument or ... If you have 6 letters which are drawn from a bag without replacement, then the probability of A (for example) being drawn on the first, second, .. , sixth selection is 1/6 in each case. Each letter would be equally likely to be selected at each time if you dont know the result of what has already been selected. A simple counting argument would make it explicit.

Your reason about it being 1 of 6 assumes that there is a single pick, not a second pick without replacement. Looks like you hit lucky that the answer was the same, but the reasoning isnt correct.

For the tree, its black/not black so you have two choices and two levels (first and second selection). You should have done that at gcse so have a go and upload if necessary.