Question 1033649
i believe your tree diagram will look something like this.
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you first draw from bag A.
the probability of getting a black marble is 7/15.
you then draw from bag B.
the probability of getting a black marble from bag B is 7/14.
the probability of first drawing a black marble from bag A and then drawing a black marble from bag B is therefore 7/15 * 7/14 = 49/210.
this can be simplified to 7/30.
here's a tutorial on how to draw tree diagrams.
<a href = "https://www.mathsisfun.com/data/probability-tree-diagrams.html" target = "_blank">https://www.mathsisfun.com/data/probability-tree-diagrams.html</a>
there are others.
just do a search for "how to draw a tree diagram" or something like that.
if you add up all the probabilities, they should be equal to 1.