Question

The total cost of 4 soaps and 5 brushes is rs 123 and total cost of 5 soaps and 4 brushes is rs 120 .what is the cost of 1 soap ?

Answer 1

let the cost of soap be x and of brushes be y
then the equations are
4x+5y=123
5x+4y=120
use elimination method
(4x+5y=123)4
(5x+4y=120)5
16x+20y=492
‐(25x+20y=600) then the sign changes

16x+20y=492
-25x-20y=-600 (20y and -20y gets cancel)
-----------------------
-9x. =-108
then x= 108÷9
x=12
hence the cost of 1 soap is 12 rupees.