Error Analysis

Find the error in the problem below
19 - 2k = 3k - 1
     +3k   +3k
19 + 1k = -1
-19           -19
k = -20

• They should have divided by 1 for the last step
• They should add 19 instead of subtracting 19
• I can not find an error
• Instead of adding 3k they should subtract 3k

Tags

CCSS.HSA.REI.A.1

Find the Error
What error did the student make when solving the equation:
1/5x + 6 = 3/5x + 5
1x + 6 = 3x + 5
-2x + 6 = 5
-2x = -1
x = 1/2

• The student found an incorrect common denominator
• The student did not multiply all terms by the common denominator
• The student did not use opposite operations appropriately
• The student did not correctly eliminate the variable from one side of the equation

Tags

CCSS.HSA.REI.A.1

CCSS.HSA.REI.B.3

5 + 2(n + 1) = 2n
Bill says the first step is to add and get
7(n + 1) = 2n

• Bill is correct
• Bill is wrong; he should have distributed the 2 first.
• Bill is wrong; he should have subtracted 5 from both sides first.
• Bill is wrong; he should have divided by 2 firat.

Tags

CCSS.8.EE.C.7B

How many solutions does the equation below have?
6(3a +1) - 30 = 3(2a - 4)

• Identity
• No Solution
• Three Solutions
• One Solution

Tags

CCSS.8.EE.C.7A

Where was the mistake made?
           5d  =    2d - 18
-2d        -2d
3d =     -18
d = 6

• Subtracted 2d instead of adding
• Should have gotten -6 when dividing -18 by 3
• Should have added 18 to both sides first
• Should have subtracted 5d from both sides first

Tags

CCSS.HSA.REI.A.1

1/2(8x-12)=x-2
4x-6=x-2
5x-6=-2
5x=4
x=4/5

• The first step is wrong; they should have divided both sides by 2.
• The second step is wrong; they should have subtracted x from both sides.
• The third step is wrong; they should have subtracted 6 from both sides.
• The last step is wrong; they should have multiplied both sides by 5.

Tags

CCSS.8.EE.C.7B