<PRE><B>Question 471953</B>
The sequence is arithmetic, so we say that


*[tex \LARGE a_2 = a_1 + c]


*[tex \LARGE a_3 = a_2 + c = a_1 + 2c], and so on.


Here, since the sum of the 1st, 3rd, 5th terms is 27, we have


*[tex \LARGE a_1 + (a_1 + 2c) + (a_1 + 4c) = 27 \Rightarrow a_1 + 2c = 9]


The sum of the second and fourth terms is


*[tex \LARGE (a_1 + c) + (a_1 + 3c) = 2a_1 + 4c = 2(a_1 + 2c)]


This is equal to 2*9 = 18 since we can substitute a_1 + 2c with 9.</PRE>