Explanation:
a probability is always desired cases over total possible cases.
the bag has 4 + 7 + 8 + 6 = 25.
so, when we pick a random M&M we have total 25 possible outcomes.
the desired cases are to pick a green or a blue M&M.
that means these are 7+8 = 15 cases.
the probability to pick one or of the desired cases is
15/25 = 3/5 = 0.6