When karen's mother got a new phone number, karen memorized it. but when she called her mother a day later, she called the old number. this is an example of interference?

The answer is a proactive interference. This is where an old data avoids the recollection of newer information. This might, for instance, happen with telephone numbers. When trying to remember a new phone number, the old phone number you have beforehand could proactively delay with the recall, to the fact when it is very hard to recall the new number.

answer; when one group has an extremely high score at pretest;