Kirsten's work is shown below:

1 x 1.75 = 1.75
10 x 1.75 = 10.75
100 x 1.75 = 100.75
1,000 x 1.75 = 1,000.75

This is the correct pattern:

1 x 1.75 = 1.75
10 x 1.75 = 17.5
100 x 1.75 = 175
1000 x 1.75 = 1,750

What was her mistake?