Mandrake Falls High School is providing a weekend course in laboratory techniques to its laboratory students. Of the students enrolled in lab classes at Mandrake, have taken the weekend course. Mandrake is evaluating the course's effectiveness by having its lab instructors record harmful lab "incidents": accidents, misuse of lab equipment, etc. The contingency table below gives a summary of the data that have been gathered so far for Mandrake's lab students. Each student is classified according to whether or not he has taken the lab techniques course and how he has performed in the lab. In the cells of the table are the respective observed frequencies. Note that three of the cells also have blanks. Determine the frequencies expected if the two variables, status regarding lab techniques course and laboratory performance, are independent.