how do i evaluate the following two expressions??

9 8 2 - 3 / +

I come up with
9 - 8 = 1 / 2 = .5 + 3 = 3.5

3 4 5 2 * - +

I come up with
3 * 4 = 12 - 5 = 7 + 2 = 9

Am I doing this right when talking of binary tree postfix expressions???