Ramanath Parimi

Step 1: Note down the given terms, and write their equivalent term in the arithmetic sequence.

EXAMPLE: 18th term = a + (n-1)d = a + (18-1)d = a + 17d

                    21st term = a + 20d.

Step 2: Equate the given terms with the equivalent terms of the arithmetic sequence. This will from the equations.

EXAMPLE: 18th term of the series is 25. Which means, a + 17d = 25

Step 3: Solve these equations (linear equations) to get the unknown values

RECALL : Solve linear equations [Q-A1.V.2]