Probability was my favourite at high school. As you said, if the...

Probability was my favourite at high school.

As you said, if the probability of success for each individual trial is 50%, then the probability of at least one being successful is 93.75%

Probability that all four trials are successful = (0.5 * 0.5 * 0.5 * 0.5) = 6.25%
Probability that at least one is successful = 100% - (0.5 * 0.5 * 0.5 * 0.5) = 93.75%

Let's have some fun here and bump up the success probability to 70% based on the fact that variations of these concoctions have been proven successful in less formal settings:-

Probability that all four trials are successful = (0.70 * 0.70 * 0.70 * 0.70) = 24.01%
Probability that at least one is successful = 100% - (0.3 * 0.3 * 0.3 * 0.3) = 99.19%

I think I prefer that one