Hello, Sam!

First block is red:A bag contains 4 red and 3 green blocks.

Three blocks are randomly selected from the bag.

Determine the probability that all three are red given that:

a) replacement occurs between the second and third selections

Second block is red: . . . . The second block replaced.

Third block is red:

Therefore:

First block is red:b) no replacement occurs

Second block is red:

Third block is red:

Therefore: