1.Corresponding terms of A.P = first and last, second and second last etc. So if an AP is 1,2,3,4,5,6 then corresponding terms are (1,6) , (2,5) , (3,4).

2.Average of the A.P = mean of the corresponding terms e.g: 1+6/2 or 2+5/2 etc

3.Sum of A.P = ( Average of A.P. ) * ( Number of terms )

4.Finding the Common difference given two terms in an A.P =If Tx and Ty are the terms in an AP at position ‘x’ and ‘y’. The common difference = > ( Ty – Tx ) = Common difference * (y-x). E.g: So if 3rd term is 8 and 8th term is 28 the common difference is (28 – 8) = d * (8-3) = > 20 = 5*d and d = 4.4