Question

Mr. Montes is writing a short, three-question, true or false quiz for his Algebra 2 classes. He had planned on using a random answer generator to determine which of true or false would be the correct answer for each quiz question, but his internet is not working. Instead, he writes each possible answer combination on a small slip of paper, folds each paper in half, and then places them in a box. Without looking, he draws one of the slips of paper.

Use what you know about counting methods and set operations to answer the following questions.
After grading the quizzes, Mr. Montes decides that his students could use some additional practice with the concepts tested. He writes a take-home assignment for his students. The assignment starts with two true or false questions and then has 3 multiple choice questions. The multiple choice questions each have 4 answer options, only 1 of which is correct. Luckily, Mr. Montes’ internet is working when he writes the quiz and he is able to use a random answer generator.
After grading the take-home assignments, Mr. Montes randomly selects 5 take-home assignments to analyze. He considers the student’s responses to the three multiple choice questions, which are as shown.
Student 1: Student 2: Student 3: Student 4: Student 5:
{C, A, C} {C, B, B} {C, B, C} {C, B, A} {C, A, A}
Amisha was too tired to work on the take home assignment Mr. Montes gave her, so she randomly selected answers without reading any of the questions. Suppose that you wanted to find the odds that Amisha answered at least 3 of the 5 questions correctly. Do you think you would use a permutation or a combination?
1. The correct responses for the multiple choice questions are, in order, C, B, and A. If Set 1 represents the subset of these students who answered C for number 1, Set 2 represents the subset of these students who answered B for number 2, and Set 3 represents the subset of students who answered A for number 3, find each of the following. Explain what each notation means in context of this scenario.
a. Set 1 ∩ Set 2
b. Set 2 ∪ Set 3
c. The complement of Set 1
2. Amisha was too tired to work on the take home assignment Mr. Montes gave her, so she randomly selected answers without reading any of the questions. Suppose that you wanted to find the odds that Amisha answered at least 3 of the 5 questions correctly. Do you think you would use a permutation or a combination?

Answer 1

There are 4 questions to answer here and the answers are given below:

1. COMBINATION

2. SET 2

3. {S2, S3, S4, S5}

4. { } OR ∅

Explanation:

The key topics here are PERMUTATION & COMBINATION and SETS & VENN DIAGRAMS.

The assignment has 5 questions in all. The options for each question are listed below and separated by commas:

1. True, False

2. True, False

3. A, B, C, D

4. A, B, C, D

5. A, B, C, D

Mr. Montes derives his answers from a random answer generator; same way Amisha generated her answers by random selection.

QUESTION 1

If you want to find the odds that Amisha got at least 3/5 of the answers correctly, would you use a permutation or a combination?

ANSWER TO QUESTION 1

You would use a combination. Note that as much as 'permutation' is distinctly defined from 'combination', in many complex cases both are used to derive the solution. In this case though, a combination is used. For each of the 5 questions, there are a number of possible answers. Questions 1 and 2 have only two possible answers (also known as options) while questions 3, 4 and 5 have four possible answers/options to choose from. Amisha can only have one set of five answers; each to each question. So this is a combination! If you want to find the odds that Amisha got at least 3 of her 5 answers correct, you would use a combination of the various possible answers to check.

QUESTION 2

Find "Set 1 ∩ Set 2" and explain the notation in the sentence.

ANSWER TO QUESTION 2

First list out relevant information:

- The correct answers to questions 3, 4 and 5 are respectively C, B, A

- The universal set consists of five students: S1, S2, S3, S4, S5 hence

Ц = {S1, S2, S3, S4, S5}

Next, enlist the elements of each defined set

Set 1: {S1, S2, S3, S4, S5} Set 2: {S2, S3, S4} Set 3: {S4, S5}

Note: Set 1 is equal to the universal set.

Now this notation "∩" means "intersect". It requires an action - checking out which elements in one set also appear in a second set and then bringing those elements to form a new set.

In the case of this question, we're to find Set 1 intersect Set 2. The elements present in Set 1 and also present in Set 2 are {S2, S3, S4}.

If you look closely, you'll observe that these are the same elements in Set 2! This brings to remembrance, one of the laws of sets:

The intersect of any subset and the universal set (recall that Set 1 happens to be equal to or have the same elements as the universal set) is equal to that subset.

So the answer to question 2 is

Set 1 ∩ Set 2 = Set 2

QUESTION 3

Find "Set 2 ∪ Set 3" and explain the notation in the sentence.

ANSWER TO QUESTION 3

The notation ∪ represents "union". This is the act of putting together the elements in two sets, to form a new set. In this activity, if an element appears in both sets, it is only written once in the new set, not twice.

So, Set 2 union Set 3 = {S2, S3, S4, S5}

As earlier stated, Student 4 isn't appearing twice in the new set.

QUESTION 4

Find the ' of Set 1 and explain the notation in this sentence.

ANSWER TO QUESTION 4

The symbol ' means "complement of a set". Finding the complement of a set is like subtracting the elements of that set from the universal set.

Since Set 1 contains the same elements as the universal set, subtracting Set 1 from the universal set will give you nothing. In this case, the complement of Set 1 is a null set!

Set 1 ' Ц = { } or ∅

where the empty bracket symbol and the slashed zero symbol represent null set.

Kudos!