Two of the solutions below have common mistakes in them, only one is correct.
• Find the two common mistakes
• Explain why they are so common and their effect
• Discuss how you can avoid these mistakes
3(x + 2) + 5 = 2x – (1 + 3x)
3(x + 2) + 5 = 2x – (1 + 3x)
3x + 6 + 5 = 2x – 1 + 3x
3x + 11 = 5x – 1
11 = 2x -1
12 = 2x x = 6
3(x + 2) + 5 = 2x – (1 + 3x)
3x + 6 + 5 = 2x – 1 – 3x
3x + 11 = -x – 1
4x + 11 = -1
4x = -12 x = -3
3(x + 2) + 5 = 2x – (1 + 3x)
3x + 6 + 5 = 2x – 1 – 3x
6 + 5 = 2x - 1 - 6x
11 = 4x - 1
12 = 4x x = 3

Study the two solutions below.
Which of them is correct?
Where are any errors?
Are these errors common? How could they be avoided?
Would you lay things out differently?
Mark stands 27 metres from the base of the Eiffel Tower as shown.
He needs to look up at an angle of 85∙24 o to look directly at the top.
How tall is the Eiffel Tower (to the nearest metre)?
27m
4.76
o
SOH CAH TOA
Tan 4∙76 o
27 tan 4∙76 o
= x x = 2∙25m 85.24
o
27m
Tan x o
= opp
Tan 85∙24 o
27 tan 85∙24 o
= adj x
27
= x x = 11∙96038166 x = 12m
85.24
o
27m

Study the four solutions below.
Three of them are incorrect. Which three?
Explain why the three wrong answers are wrong.
What could someone writing these be thinking?
Put these decimals in order, smallest first:
0.505, 0.52, 0.052, 0.55555, 0.520, 0.025, 0.2
0.2, 0.52, 0.025, 0.052, 0.520, 0.505, 0.5555
0.2, 0.025, 0.052, 0.52, 0.520, 0.505, 0.5555
0.025, 0.052, 0.2, 0.505, 0.52, 0.520, 0.5555
0.025, 0.052, 0.505, 0.520, 0.2, 0.52, 0.5555