Question

There are three bags. The first bag has two blue rocks. The second bag has two
red rocks. The third bag has a blue and a red rock. All bags are labeled but all
labels are wrong. You are allowed to open one bag, pick one rock at random, see
its color and put it back into the bag, without seeing the color of the other rock.
How many bags do you need to open to re-label all three bags correctly? Explain
your logic.

Answer 1

Only once. Open the bag with label BR. Then if u get blue in that the correct label is Blue. And since blue is fixed and other two labels are wrong, interchange those labels.  Similarly, if u get red the correct label will ne red and the remaining two labels will be interchanged.