The amount of meat needed is proportional to the number of guests. We can set up a ratio based on the information given:
If there are 25 guests, the caterer needs 40 pounds of meat. Therefore, we can write the ratio of meat to guests as follows:
\[ \frac{40 \text{ pounds}}{25 \text{ guests}} = \frac{x \text{ pounds}}{100 \text{ guests}} \]
To find \( x \), we can cross-multiply:
\[ 40 \times 100 = 25 \times x \]
This simplifies to:
\[ 4000 = 25x \]
Now, divide both sides by 25:
\[ x = \frac{4000}{25} = 160 \]
Therefore, if there are 100 guests, the caterer should order 160 pounds of meat.