Question

The cost of 4 pens and 4 pencil boxes is rs 100. three times the cost of a pen is rs 15 more than thecost of a pencil box. form the pair of linear equations for the above situation. find the cost of a pen anda pencil box.

Answer 1

let cost of 1 pen be xcost of 1 pencil box be yATQ== 4x+4y=100--------=4x+4y-100=0.........13x=y+15 -----=3x-y-15=0...........2..from 1 nd 2 by using elimination method
3(4x+4y-100).........=12x+12y-3004(3x-y-15)..............=12x-4y-60.12y+4y-300+60=0=16y-240=016y=240y=240/16y=15.....3. substituting value of y (3 in 2)3x-15-15=03x-30=03x=30x=10..