HKIMO 2018 Grade 5 National Final (Heat) Set 03 Question 21

A staircase has 9 steps. Alice can climb 1, 2 or 3 steps at a time. The fourth step is broken and cannot be landed on. How many ways can she climb the stairs?

Source glossary (English–Vietnamese): Each time: mỗi lần; Destroyed: bị hỏng; Way: cách đi.