Chenchen actually climbed four steps from the first floor to the fifth floor. He was on the first floor from the beginning, so he didn't have to climb the first floor. Minus one from the fifth floor is the fourth floor. It takes 24 seconds to climb from the first floor to the fifth floor in the morning, and it takes 6 seconds for him to climb every floor.

The idea of climbing stairs to solve primary school math problems is that there are no stairs on the ground floor, so it cannot be calculated directly according to the number of floors. The key is to know the number of steps. You can draw a conclusion by subtracting one from the total number of floors in the corresponding time.