Question

Ivan found the change in a scale factor. His work is shown below. What error did Ivan make?

Answer 1

Ivan wrote the ratio incorrectly. The ratio should be written as the old length to the new length, so it should be 35/10, which reduces to 7/2. When going from larger to smaller dimensions, the change in the scale factor is a ratio that looks like an improper fraction, with a larger number in the numerator and a smaller number in the denominator.

Answer 2

Scale factor is:
factor = (new length) / (old length)
Ivan correctly inserted numbers and correctly divided these two numbers by 5.

There is no error in the shown picture.