If 12x + 13y = 29 and 13x + 12 y = 21, find x + y.

Soln:  Let 12x + 13y = 29 ------------ eq. no. 1

and 13x + 12 y  = 21 ----------- eq. no. 2

Adding eq. 1 and eq. 2

12x + 13y = 29 13x + 12y = 21 25x + 25y = 50

∴ 25 (x + y ) = 50

∴ x + y = 50/25

∴ x + y = 2

Answer: The value of (x+y) = 2.