Let's start by making a ratio comprised of the pieces of cheese to number of guests.
Ratio = 8 pieces of cheese : 10 guests
Now, the problem asks us to complete a ratio. We know the number of guests but not how many pieces of cheese are needed.
Incomplete Ratio = ? pieces of cheese : 30 guests
For every 10 guests, there are 8 pieces of cheese. 30 guests = 3 sets of 10 guests (10 x 3 = 30). So, 8 x 3 = 24.
Answer: 24 pieces of cheese
Hope this helps!