16

Question 2: What is the number of matchsticks in the nth figure?

Regularly, the last number is 5 matchsticks more than the previous number, and the nth number is 5 (n- 1) more than the previous number, that is, 6+5(n- 1) = 5n+ 1.

Question 3: What is the number of matchsticks in the picture 100th?

5× 100+ 1=50 1

Question 4: Can the number of matchsticks be 20 10? If so, what is n? If not, why?

No, because 5n+ 1 is definitely not a multiple of 5, and 20 10 is a multiple of 5.