Students were asked to use the distributive property to write an equivalent expression for the expression 8−3(2+4k).
Their work is shown below. Identify the student with the correct work. For the answers that are incorrect, explain where the students made mistakes.
Student 1
8−3(2+4k)
8−6+12k
2+12k
Student 2:
8−3(2+4k)
8−6−12k
2−12k
Student 3:
8−3(2+4k)
8−6−12k
2−12k
−10k
The correct student is Student 1.
Student 1 correctly applied the distributive property by multiplying -3 by both 2 and 4k within the parentheses. This resulted in the expression 8−6+12k.
Student 2 made a mistake by incorrectly distributing the negative sign in front of the 12k. Instead of subtracting 12k, they added it. This resulted in the expression 8−6−12k, which is incorrect.
Similarly, Student 3 made the same mistake as Student 2. They incorrectly distributed the negative sign and subtracted 12k instead of adding it. This resulted in the expression 8−6−12k, which is incorrect.
Student 3 also made an additional mistake by subtracting 10k at the end, which is not part of the original expression.
Therefore, Student 1 is the only student with the correct work.
The student with the correct work is Student 1.
To distribute the -3, Student 1 correctly distributed it to both terms inside the parentheses:
-3 * 2 = -6
-3 * 4k = -12k
Then, they simplified the expression by combining like terms:
8 - 6 + 12k = 2 + 12k
This is the correct equivalent expression for 8 - 3(2 + 4k).
Both Student 2 and Student 3 made mistakes in their work.
Student 2 incorrectly distributed the -3 by changing the signs of both terms inside the parentheses. It should have been:
-3 * 2 = -6
-3 * 4k = -12k
Then, they simplified the expression by combining like terms:
8 - 6 - 12k = 2 - 12k
So, Student 2's work is incorrect.
Student 3 also made the same mistake as Student 2. They distributed the -3 by changing the signs of both terms inside the parentheses:
-3 * 2 = -6
-3 * 4k = -12k
Then, they simplified the expression by combining like terms:
8 - 6 - 12k = 2 - 12k
After that, Student 3 further simplified the expression by subtracting 10k:
2 - 12k - 10k = 2 - 22k
So, Student 3's work is incorrect.