Yes, because 3/12 can ne simplified to 1/4 and one fourth is less than 2/3 so therefore 3/12 is less than 2/3. Think of it as a pizza, if you cut the pizza into twelve pieces and eat three and then you take another pizza and cut it into three pieces and eat two, which pizza has less eaten?
Well, when you simplify 3/12 it equals 1/4 so if you multiply that by 3 and multiply 2/3 by 4 to get common denominators, you have 3/12 and 8/12, so yes, 3/12 is less than 2/3. I hope this helps cx