Not able to understand the explanation of following question.
Q
An arithmetic progression of n ( n > 25 ) terms has only integers in it. The average of the first four terms is 14 and the average of the last four terms is 52. What is the common difference?
A
1
B
2
C
18
D
19
Explanation
Let the first term be a and common difference be d. The average of the first four terms is a+1.5d = 14. The average of the last 4 terms is a+(n-2.5)d = 52. Subtracting, we get, (n-4)d = 38. Since n>25, the only possibility is n-4 = 38 and d = 1.