Mark was thinking of a number Mark added 11 to it then doubles it and gets a answer of 40.5

9.25

Step-by-step explanation:

Mark doubled the number so we can divide 40.5 by 2 which is 20.25

Then we can subtract 11 from 20.25 because Mark added 11 to the number.

what is the original number? you forgot to add it.

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.