Question

The work of a student to solve a set of equations is shown below:

Equation 1: m = 6 + n
Equation 2: 2m = 8 + 8n


Step 1: −2(m) = −2(6 + n)
2m = 8 + 8n

Step 2: −2m = −12 − 2n
2m = 8 + 8n

Step 3: −12 − 2n = 8 + 8n

Step 4: −20 = 10n

Step 5: n = −2


In which step did the student first make an error?
Step 2
Step 3
Step 4
Step 5

Answer 1

Hint there is a mistake in adding the 2 equations

Answer 2

sorry gotta go now

Answer 3

either a or b

Answer 4

I think

Answer 5

plz help

Answer 6

It looks to be in Step 3 I think. The student seems to let the two equations (from Step 2) equal one another rather than adding them together. In doing so, they would have to be assuming that -2m = 2m (i.e. m = 0), which cannot be assumed here when solving these equations.

-2m = -12 - 2n
2m = 8 + 8n

If we add these two equations together, we should get:

0 = -4 + 6n
=> 6n = 4
=> n = 6/4

Answer 7

thx