Answer: They would use 300 pickles for 100 hamburgers.
Explanation:
Given: McDonald's use 9 pickles for 3 hamburgers
⇒Ratio of hamburger to pickles=3:9
Ratio in simplest from 3:9=
=1:3
⇒McDonald's use pickles for 1 hamburger.
Now Number of pickles for 100 hamburgers= 100×3=300
Therefore, They would use 300 pickles for 100 hamburgers.