In a school the odds of a student speaking spanish are $30\%$. If we select $3$ random students, what are the chances of at least one of them speaking spanish?
So, I saw this question and tried to solve it, seemed like an easy question but I was wrong and still not sure why.
Apparently the correct answer is $65.7\%$ ($100\% - 70\% \cdot 70\% \cdot 70\%$).
My first attempt at solving I figured $90\% = 3 \cdot 30\%$ (I just need $1$ student to know spanish, and I have $3$ "chances").
What is the corrent approach for this?

It is better to think about the complement.  The opposite of selecting at least 1 Spanish speaker is to pick all three students who do NOT speak Spanish.  Can you compute this probability? Then your desired answer is just 100% minus this answer.
