(b) Amba is working out the size of an interior angle of a regular octagon.
Not drawn accurately
Her method is \(\qquad\) Interior angle \(= 360 \div 8\)
Is her method correct?
Tick a box.
Yes
No
Give a reason for your answer. [1 mark]
Mark scheme (a)
Answer
Mark
Comments
\(180 \div 3\) or 60
M1
oe eg \(60 + 60 + 60 = 180\)
\((180 - 28) \div 2\) or \(152 \div 2\) or 76
M1
oe eg \(76 + 76 + 28 = 180\)
\(180 -\) their \(60 -\) their 76
M1dep
oe eg \(44 + 60 + 76 = 180\) dep on M1M1
44
A1
Additional guidance
60 or 76 seen in appropriate place on diagram or in working scores one mark for each
Answer 44 not from wrong working
M3A1
\(180 - 28 \div 2\) unless recovered
2nd M0
Mark scheme (b)
Answer
Mark
Comments
No and gives correct reason
B1
eg it should be \(180 - (360 \div 8)\) it should be \(1080 \div 8\) this gives the exterior (not the interior) angle it should be obtuse not acute accept any unambiguous indication of No
Additional guidance
A correct reason may be
showing a correct method
correction of her method (error and replacement shown)
correction of her answer (answer and replacement shown)
No, It should be 135 not 45 (3)
B1
No, It should be 1080 not 360 (2)
B1
No, because the interior angles should be 1080 not 360 (2)
B1
No, she needs to subtract her answer from 180 (1)
B1
No, \(((8 - 2) \times 180) \div 8\) (1)
B1
No, It should be \(((n - 2) \times 180) \div 8\) (doesn’t use \(n = 8\))
B0
Any numbers quoted must be correct but ignore other non-contradictory statements
eg No, It should be 720. She’s worked out the exterior angle
B0
No, There’s not 360 in an octagon or No, Angles in an octagon do not add up to 360
