Write the missing number under each tick mark on the number line

ok as you can see we have a line between 18 and 30 and the difference is 12 write divide 12 by 2 to get six add 18 + 6 to get 24 and 30 + 6 get 36 that's the answer

answer: all of the odd numbers were opened

the first person was the one that was opening all of the lockers. since one is odd, this causes all of the odd number lockers to be opened in the end.