Question

The cost of a bottle of water is (w – 1) cents.

The cost of a bottle of milk is (2w – 11) cents.
A certain number of bottles of water costs $4.80.
The same number of bottles of milk costs $7.80 .
Find the value of w

Answer 1

w= 25

Explanation:

Cost of water= (w -1)¢

Cost of milk= (2w -11)¢

Let the certain number be x.

x(w -1)¢= 480¢ -----(1)

x(2w -11)¢= 780¢ -----(2)

From (1):

wx -x= 480 -----(3)

From (2):

2wx -11x= 780 -----(4)

(3) ×2:

2wx -2x= 960 -----(5)

(5) -(4):

(2wx -2x) -(2wx -11x)= 960 -780

Expand:

2wx -2x -2wx +11x= 180

9x= 180

Divide both sides by 9:

x= 180 ÷9

x= 20

Substitute x= 20 into (3):

w(20) -20= 480

20w -20= 480

20w= 480 +20

20w= 500

w= 500 ÷20

w= 25