FT ‘their \(\dfrac{\text{vertical diff}}{\text{horizontal diff}}\)’; must be negative; allow improper fractions NB allow full marks if calculus method used.
Mark scheme (b)
Scheme
Marks
Comments
(i) Summation of areas of strips
S1
e.g. trapezium rule or equivalent attempted with trapezia/triangles/rectangles
(\(v\) values = ) (0) 16, 24, (24, 16, 0) si
B1
Ignore extra correct \(v\) values for this mark; accept mid-ordinates 9, 21, 25, (21, 9)
Correct calculation for the area using 5 strips
M1
FT ‘their \(v\)-values’ e.g. \(2\left(\dfrac{1}{2}\times2\times16 + \dfrac{1}{2}\times2\times(16+24)\right) + 2\times24\) or \(2\left(\dfrac{1}{2}\times2\times16 + 2\times20 + 1\times24.5\right)\) or \(2\left(\dfrac{1}{2}\times2\times16 + \dfrac{1}{2}\times2\times(16+24)\right) + 2\times25\) (using mid-ordinates) \(2(9\times2) + 2(21\times2) + 25\times2\)
M0 if only using rectangles except for use of mid-ordinate rule approaches
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