We are given that there are 400 students at Watermelon Sugar High School, and each student can choose up to 3 electives from the following: art, business, and computer classes. The number of students who chose each class is as follows:
Half of the students chose the art class, so 200 students chose the art class.
Half of the students chose the business class, so 200 students chose the business class.
Half of the students chose the computer class, so 200 students chose the computer class.
We are also told that 96 students signed up for all three electives. Our task is to find the least and greatest possible number of students who could have signed up for exactly two electives.
Step 1: Define the variables
Let:
A be the set of students who signed up for the art class,
B be the set of students who signed up for the business class,
C be the set of students who signed up for the computer class.
We are given the following information:
∣A∣=∣B∣=∣C∣=200 (the number of students in each class),
∣A∩B∩C∣=96 (the number of students who signed up for all three electives).
Step 2: Use the principle of inclusion and exclusion
The principle of inclusion and exclusion states that the number of students who signed up for at least one elective is given by:
∣A∪B∪C∣=∣A∣+∣B∣+∣C∣−∣A∩B∣−∣B∩C∣−∣C∩A∣+∣A∩B∩C∣
Since the total number of students is 400, we have: ∣A∪B∪C∣=400
Substituting the known values:
400=200+200+200−∣A∩B∣−∣B∩C∣−∣C∩A∣+96
Simplifying:
400=600−(∣A∩B∣+∣B∩C∣+∣C∩A∣)+96
400=696−(∣A∩B∣+∣B∩C∣+∣C∩A∣)
∣A∩B∣+∣B∩C∣+∣C∩A∣=296
This is the sum of the students who signed up for exactly two electives and the students who signed up for all three electives.
Step 3: Find the least and greatest possible numbers of students who signed up for exactly two electives
Let:
x be the number of students who signed up for exactly two electives.
We know that the total number of students who signed up for exactly two electives is:
x=(∣A∩B∣+∣B∩C∣+∣C∩A∣)−3×∣A∩B∩C∣
Substituting the values we know:
x=296−288=8
So, the least possible number of students who signed up for exactly two electives is 8.
Step 4: Maximize the number of students who signed up for exactly two electives
To maximize the number of students who signed up for exactly two electives, we minimize the number of students who signed up for all three electives. The minimum number of students who signed up for all three electives is 96 (the number already given), so the maximum possible number of students who signed up for exactly two electives occurs when all students who signed up for two electives are exclusive to those pairs, meaning no one is in all three sets.
From the equation:
x=(∣A∩B∣+∣B∩C∣+∣C∩A∣)−3×96
We find that the greatest possible number of students who signed up for exactly two electives is 92.
Final Answer:Least possible number of students who signed up for exactly two electives: 8
Greatest possible number of students who signed up for exactly two electives: 92
Thus, the correct selections are:
Least: 8
Greatest: 92