Step by step subtraction of 17 - 1.2

= 15.8

Summary of Work:

 610

 17.0

−01.2

 15.8

Step by Step:

Working each column from right to left

 17.0

−01.2

 .

2 is greater than 0 so you must regroup:

Take 1 from 7, so 7 becomes 6.

Add 10 to 0, so 0 becomes 10.

 610

 17.0

−01.2

 .

10 minus 2 is 8

 610

 17.0

−01.2

 .8

6 minus 1 is 5

 610

 17.0

−01.2

 5.8

1 minus 0 is 1

 610

 17.0

−01.2

 15.8

this is a direct variation proportion. y = kx

y is the total amount due, k is the constant of variation, and x is the number of texts sent.

plug in the 3.20 and the 16 to solve for the "k". this is the constant of proportionality. it is the value that will not change.

3.20 = k(16). solving you get $.20 per text.

the equation would then be y = .20x