Let the marks of the students in class 1 be

the average of these 12 marks is 90, so

which means

similarly, let

be the marks of the students in the second class,
so

which means

The 32 students averaged:
Answer:
Triangles.
Step-by-step explanation:
Answer:
The altitude will begin at angle D and go in a straight line downwards.
The perpendicular bisector will be a straight line going from one corner to the other corner, not directly downwards.
Answer: The answer is (-7,12)
Step-by-step explanation:
Problem 11) Start with set U = {1,2,3,4,5} and cross off 1,2,3 to be left with A' = {4,5}. We basically erase everything found in set A. You have the correct answer. Nice job.
Problem 12) Start with U = {1,2,3,4,5} and erase '5' to be left with {1,2,3,4}. So B' = {1,2,3,4}. You are correct here as well.
I can't help with the other problems since either letters, numbers or symbols are missing. Please make a new post and provide those updates.