O-LevelMathematicsGeometry4024/12 · Oct/Nov 2015 · Q193 Marks
Solve a geometric problem involving angles resulting in 12.
- Solve a geometric problem involving angles resulting in 12.[3]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2015). The mark or mark type is shown in brackets.
- [3*] 12 WWW
- M1 for starting to solve the problem correctly, using exterior angles sum = 360 or interior angles sum = 180 × 3x -360 oe and A1 for correct equation(s) in their variable(s), e.g. 2x(180 – 155) + x(180 – 140) = 360 oe or 155 x 2x + 140 x x = 180 x 3x-360 oe
- (n-2)×180 = n× (2x155+140)/3 oe
- n× [180- (2×155+140)/3 ] = 360 oe
- 450x = 180(n-2) and n = 3x
- or M2 for a complete method, clearly explained, that does not use algebra
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