Understanding complementary events can be tricky for Year 7 students.

1. Hard to Understand: Many students find it tough to realize that complementary events are just the situations when something does not happen.

2. Frustration with Calculations: Figuring out the probability of a complement can be confusing. It's shown as $P(A') = 1 - P(A)$. This can be especially hard when working with fractions or decimals.

3. Finding Solutions: To make things easier, regular practice, using visual tools like Venn diagrams, and examples from everyday life can really help students get better at understanding and calculating probabilities.