Ask any elementary school teacher, and she or he will tell you that comparison problems are much harder for most kids than operations with other actions. For example, fourth-grade-teacher Jennifer Clerkin Muhammad asked her students to draw a picture of this problem from Investigations:
Darlene picked 7 apples. Juan picked 4 times as many apples. How many apples did Juan pick?
Her students are pros at representations and skillful multipliers, but we saw a lot of this: