The ratio of almonds to raisins is given as 4:3. This means that for every 4 almonds, there are 3 raisins.
If there are 600 almonds in the bag, we can set up a proportion to find the number of raisins. Let \( r \) be the number of raisins.
Using the ratio: \[ \frac{4}{3} = \frac{600}{r} \]
Now we can cross-multiply to solve for \( r \): \[ 4r = 3 \times 600 \]
Calculating the right side: \[ 3 \times 600 = 1800 \]
So we have: \[ 4r = 1800 \]
Now, divide both sides by 4: \[ r = \frac{1800}{4} = 450 \]
Thus, the number of raisins in the bag of trail mix is: \[ \boxed{450} \]