Unconditional probability I understand the tree diagram but my answer is wrong. 
Urn I contains three red chips and one white chip. Urn II contains two red chips and two white chips. One chip is drawn from each urn and transferred to the other urn. Then a chip is drawn from the first urn.What is the probability that the chip ultimately drawn from urn I is red?

Hint:
Urn I should end up with the following chips given the color of chip being taken from I and II and transferred accordingly.
$$
\begin{array}{c|c|}
Grid & \text{Red(I)} & \text{White(I)} \\
\hline
\text{Red(II)} & \text{3r+1w}& \text{4r} \\
\text{White(II)} & \text{2r+2w} & \text{3r+1w} 
\end{array}
$$
