In which of the following situations does the list of numbers involved make an arithmetic progression, and why?

(i) Fare for first km=Rs.15
Fare for second km=Rs (15+8)=Rs.23
Fare for third km=Rs (23+8)=Rs.31
Here, each subsequent term is obtained by adding a fixed number(8) to the previous term. Hence, it is in A.P
(ii) Let us assume, initial quantity of air=1
Quantity removed in first step=1/4
Remaining quantity after first step=1−1/4=3/4
Quantity removed in second step=(3/4)×(1/4)=3/16
Remaining quantity after second step=(3/4)−(3/16)=9/16
Here, each subsequent term is not obtained by adding a fixed number to the previous term. Hence, it is not an AP
(iii) Cost of digging of 1st meter=150
Cost of digging of 2nd meter=150+50=200
Cost of digging of 3rd meter=200+50=250
Here, each subsequent term is obtained by adding a fixed number(50) to the previous term. Hence, it is an AP
(iv) Amount in the beginning=Rs.10000
Interest at the end of 1st year @8%