Four students are in a class. Compute the probability of the event Four students are in a class. Compute the probability of the event that:

1) at least one of them is born on a Saturday

2) at least 2 of them are born on the same day of the week(e.g on a Sunday)

3) all four of them are born during the weekend(i.e on Saturday or Sunday)

These are my solutions:

1) 1/7 + 1/7+ 1/7 + 1/7 = 57%

2) 1/7 * 1/7 = 2.04%

3) 2/7 * 2/7 * 2/7 * 2/7 = 0.66%

Are these correct? 

Thank you
Some hints:


What is the negation of the first statement?  (If the statement is "At least one was born on a Saturday," what is the opposite of that?)
Let's call one statement $Q$ and its negation $\neg Q$.  Then, $P(Q) = 1 - P(\neg Q)$.
What is the negation of the second statement?
I was thinking of this for the first one:

53 saturdays in a year -> 4 people in a class 

1/53 + 1/53 + 1/53 + 1/53 =7.5%