A laboratory records the concentration of a chemical in a solution every half-hour. The readings form an arithmetic progression. The concentration at the first reading is 5.0 g L−1 and at the 9th reading it is 2.8 g L−1.
a. (i) Find the common difference of the progression.
b. (ii) Obtain an expression for the concentration Cn at the nth reading.
c. (iii) After how many readings will the concentration reach exactly 1.0 g L−1, if at all?