O-LevelAdditional MathematicsSeries4037/12 · May/June 2011 · Q24 Marks
The coefficient of x³ in the expansion of (2 + ax)⁵ is 10 times the coefficient of x in the expansion of (1 + (ax/3))⁴. Find the value of a.
- (a)The coefficient of x³ in the expansion of (2 + ax)⁵ is 10 times the coefficient of x in the expansion of (1 + (ax/3))⁴. Find the value of a.[4]
Mark scheme
Marking points from the official mark scheme (May/June 2011). The mark or mark type is shown in brackets.
- ⁵C₃2²a³ = (10)⁴C₁(a²/9); B1 for ⁵C₃2²a³, B1 for ⁴C₁(a²/9)
- M1 for a relationship between the 2 coefficients and attempt to solve
- a = 1/6; A1
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