To find out how many packets of sheet music the chorus students decided to share, we need to calculate \( \frac{3}{8} \) of 24 packets.
The calculation is as follows:
\[ \frac{3}{8} \times 24 = \frac{3 \times 24}{8} = \frac{72}{8} = 9 \]
So, they shared 9 packets.