When Xiaohong climbed from the first floor to the second floor, Xiaoming had climbed to the third floor.

2- 1= 1、3- 1=2

That means Xiao Ming is twice as fast as Xiao Hong.

When Xiaohong climbed to the fifth floor, Xiaoming had climbed to the ninth floor.

5- 1=4、4×2+ 1=9