CAIE P1 2024 November — Question 1 4 marks

Exam BoardCAIE
ModuleP1 (Pure Mathematics 1)
Year2024
SessionNovember
Marks4
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicBinomial Theorem (positive integer n)
TypeSingle coefficient given directly
DifficultyModerate -0.3 This is a straightforward binomial expansion problem requiring identification of a specific term using the general term formula, solving for k, then finding another coefficient. It's slightly easier than average as it involves only one unknown constant, basic algebraic manipulation, and standard binomial coefficient calculations with n=4. The two-part structure is routine for this topic.
Spec1.04a Binomial expansion: (a+b)^n for positive integer n

In the expansion of \(\left(kx+\frac{2}{x}\right)^4\), where \(k\) is a positive constant, the term independent of \(x\) is equal to 150. Find the value of \(k\) and hence determine the coefficient of \(x^5\) in the expansion. [4]

Question 1:
AnswerMarks
12
2
Identify correct term and obtain 6(kx)2  
AnswerMarks Guidance
xM1 4!
Needs numerical coefficient or , not 4C .
2
2!2!
5
Equate to 150 and obtain k =
AnswerMarks Guidance
2A1 5
Ignore –
2
2
4(kx)3
Identify correct term  with their value of k
AnswerMarks Guidance
xM1 4!
Needs numerical coefficient or .
3!1!
AnswerMarks Guidance
Obtain coefficient 125A1 Accept 125x2as final answer.
4
AnswerMarks Guidance
QuestionAnswer Marks
Question 1:
1 | 2
2
Identify correct term and obtain 6(kx)2  
x | M1 | 4!
Needs numerical coefficient or , not 4C .
2
2!2!
5
Equate to 150 and obtain k =
2 | A1 | 5
Ignore –
2
2
4(kx)3
Identify correct term  with their value of k
x | M1 | 4!
Needs numerical coefficient or .
3!1!
Obtain coefficient 125 | A1 | Accept 125x2as final answer.
4
Question | Answer | Marks | Guidance
In the expansion of $\left(kx+\frac{2}{x}\right)^4$, where $k$ is a positive constant, the term independent of $x$ is equal to 150.

Find the value of $k$ and hence determine the coefficient of $x^5$ in the expansion. [4]

\hfill \mbox{\textit{CAIE P1 2024 Q1 [4]}}