Question 9 - A-Level Maths

Exam Board	Edexcel
Module	C1 (Core Mathematics 1)
Topic	Arithmetic Sequences and Series

find the value of \(x\),
find the expected value of sales in the eighth month,
show that the expected total of sales in pounds during the first \(n\) months is given by \(k n ( 51 - n )\), where \(k\) is an integer to be found.
Explain why this model cannot be valid over a long period of time.