Why does Slotted Aloha work?

So the way I understand it, if station A and station B, for example, try to transmit a frame at the same slot, a collision occurs, leading to an attempt at the next slot. But wouldn’t the algorithm just repeat itself? The same two stations would try again on the second slot and it would still cause a collision. Also, it means that the first slot would remain unused.

Am I understanding it wrong?

ALOHA – Throughput and probabilities

I have a few questions regarding slotted-ALOHA. Assume a network have 25 users and transmission request probability = 0.25.

1) What is the throughput and what is the probability that a user will successfully transmit a frame after three unsuccessful attempts? I have managed to calculate the throughput as 0.00627. But the major problem is the probability to succeed after 3 attempts. Should I use these two formulas?

$ $ n_a = \sum_{n=0}^\infty n(1-p_a)^n p_a $ $

$ $ n_a = \frac{1-p_a}{p_a} $ $

2) What is the average number of unsuccessful attempts before a user can transmit a frame in the above problem?

Can somebody assist me?

Best regards