Let P be the statement "A student got all the multiple choice questions right on the exam".
Let Q be the statement "A student received an A on the exam".
Ms. Carroll's promise can be written as a logical implication:
P
Q
This means "If a student got all the multiple choice questions right, then the student received an A".
We are looking for a statement that necessarily follows logically from P
Q. This means we are looking for a statement that must be true whenever P
Q is true. Let's apply this to the student Lewis. Let
be "Lewis got all the multiple choice questions right" and
be "Lewis received an A". The given statement for Lewis is
.
Now let's examine each option:
A: "If Lewis did not receive an A, then he got all of the multiple choice questions wrong."
This statement is of the form
, where
is the statement "Lewis got all of the multiple choice questions wrong".
The negation of
(Lewis got all MC questions right) is
(Lewis got at least one MC question wrong).
The contrapositive of
is
. This means if Lewis did not receive an A, then he got at least one MC question wrong.
Getting all questions wrong (
) implies getting at least one question wrong (
), but getting at least one question wrong (
) does not imply getting all questions wrong (
).
So,
is true, but
is not necessarily true. Lewis could have missed just one question and not received an A.
B: "If Lewis did not receive an A, then he got at least one of the multiple choice questions wrong."
This statement is of the form
.
As mentioned above,
is the negation of
("Lewis got all the multiple choice questions right"). The negation is indeed "Lewis got at least one of the multiple choice questions wrong."
The statement
is the contrapositive of the original statement
. The contrapositive is logically equivalent to the original implication.
Therefore, statement B necessarily follows logically.
C: "If Lewis got at least one of the multiple choice questions wrong, then he did not receive an A."
This statement is of the form
.
This is the inverse of the original statement
. The inverse is not logically equivalent to the original statement.
Ms. Carroll's promise only states what happens if Lewis gets all questions right. It does not state what happens if he gets any wrong. He might still get an A based on other criteria or parts of the exam.
Therefore, statement C does not necessarily follow logically.
D: "If Lewis received an A, then he got all of the multiple choice questions right."
This statement is of the form
.
This is the converse of the original statement
. The converse is not logically equivalent to the original statement.
Ms. Carroll's promise guarantees an A if all MC questions are right, but it doesn't exclude other ways of getting an A. Lewis might have received an A even if he missed some MC questions.
Therefore, statement D does not necessarily follow logically.
E: "If Lewis received an A, then he got at least one of the multiple choice questions right."
This statement is of the form
, where
is "Lewis got all of the multiple choice questions wrong". So
is "Lewis got at least one MC question right".
Does
logically imply
?
Consider a scenario where Lewis got all MC questions wrong (
is true). In this case,
("Lewis got all MC questions right") is false. The implication
is therefore true (since False
Anything is true). Now, suppose Lewis still received an A (
is true), perhaps due to exceptional performance on other parts of the exam. In this scenario,
is true,
is true, and
is true. Statement E says
. But we have
true and
false (since
is true). So
is false in this scenario.
Therefore, statement E does not necessarily follow logically.
The only statement that is logically equivalent to the original statement is the contrapositive. Statement B is the contrapositive.
Final Answer: The final answer is 