When a student Joe, weighing 40 kg, joins a group of students whose average weight is 30 kg, the average weight goes up by 1 kg. Subsequently, if two students, excluding Joe, leave the group the average weight comes back to 30 kg. What is the difference between the average weight of the two students who left and the weight of Joe?	Choose one.
A) 5 kg
B) 11 kg
C) 30 kg
D) 36.5 kg
E) 71 kg

Rationale: "after two persons leave the group the average remains the same . that means the weight of the two persons = 40 + 30 = 70 so , the average the two persons = 35 that gives the answer 40 - 35 = 5 answer a"
Answer: A