Answer
$\frac{41}{96}$, or $\approx 0.427$
Work Step by Step
The probability of at least 2 people having the same astrological sign is the same as 1 minus the probability of no one having the same astrological sign (everyone having a different sign).
The probability of no one having the same sign is $ 1 \times \frac{11}{12} \times \frac{10}{12} \times \frac{9}{12} = \frac{55}{96}$, so the probability of at least 2 people having the same sign is $1 - \frac{55}{96} = \frac{41}{96}$.
