Step 1: Calculate the probability of hitting the target.
The probability of A hitting the target is \( \frac{3}{5} \), the probability of B hitting the target is \( \frac{2}{5} \), and the probability of C hitting the target is \( \frac{3}{4} \).
Step 2: Find the probability of missing the target.
The probability of A missing the target is \( 1 - \frac{3}{5} = \frac{2}{5} \), the probability of B missing is \( 1 - \frac{2}{5} = \frac{3}{5} \), and the probability of C missing is \( 1 - \frac{3}{4} = \frac{1}{4} \).
Step 3: Calculate the probability of exactly one hit.
The probability of exactly one hit is the sum of the probabilities of the events where exactly one of them hits and the others miss.
\[
P(\text{exactly 1 hit}) = P(\text{A hits, B misses, C misses}) + P(\text{A misses, B hits, C misses}) + P(\text{A misses, B misses, C hits})
\]
This can be computed, and the final probability for at least two hits is \( \frac{63}{100} \).
Final Answer:
\[
\boxed{\frac{63}{100}}
\]