The probability of any event to happen is determined by the following formula: nr of favorable cases / nr of possible cases. For example, the chance of getting a 6 when rolling a dice is 1/6 (only one case is favorable out of six).
I really don’t know the rules of mega millions lottery, or the way it works, but i’m sure the formula will help
I often wonder why questions are asked here that require less than a minute to find the answer somewhere else on the Internet!
And usually a more complete and correct answer.
Your answer is a bit involved, though well explained at either of the two websites below.