Question

Some students are trying to write an expression with fewer terms that is equivalent to 8 - 3(4 - 9x). Noah says, "I worked the problem from left to right and ended up with 20 - 45x." 8 - 3(4 - 9x) 5(4 - 9x) 20 - 45x Lin says, "I started inside the parenthesis and ended up with 23x." 8 - 3(4 - 9x) 8 - 3(-5x) 8 + 15x 23x Jada says, "I used the distributive property and ended up with 27x - 4." 8 - 3(4 - 9x) 8 - (12 - 27x) 8 - 12 - (-27x) 27x - 4 Andre says, "I also used the distributive property, but I ended up with -4 - 27x." 8 - 3(4 - 9x) 8 - 12 - 27x -4 - 27x Do you agree with any of them? Explain your reasoning.

Answer 1

Answer: Yes I agree with Jada. His approach is correct.

Step-by-step explanation: The question requires the student to write an equivalent equation with fewer terms. Nonetheless, this does not prevent applying a mathematically correct approach.

(1) Noah is wrong and the reason is that the initial step is mathematically incorrect. The expression on the right hand side reads 3(4 - 9x), therefore starting with "8 - 3" is very wrong. The right step was to take one side which is 8 and take the other side which is 3(4 - 9x).

(2) Lin is wrong and the reason is that she started inside the parenthesis and this also is mathematically incorrect. The digits inside the parenthesis are "not like terms" and hence calculating 4 - 9x = -5x is very incorrect (the same way you cannot correctly calculate 500 metres minus 200 inches. You must make sure they are both in meters or in inches, that is both must be like terms).

(3) Jada is very correct in using the distributive property and ended up with the only correct solution. The digits on the right hand side of the expression  was solved first and that resulted in -12 + 27x. The reason being that the number outside the parenthesis which is -3, multiplied both digits inside the parenthesis. The minus sign had a major effect, and after simplifying the right hand side the expression now becomes;

8 - 12 + 27x

Since the like terms are 8 and 12, you can simplify further to become

- 4 + 27x OR the expression can be rearranged as 27x - 4

(4) Andre is not correct and the reason is that although he used the distributive property, he made a slight mistake while solving for the right side of the expression. What Andre did was

-3(4 - 9x)

-12 - 27x

Remember that when a negative value multiplies another negative value the answer is positive. Therefore -3 times -9x should have been +27x, just like Jada did as shown above.

From that point onward, his answer would be incorrect.