Answer: 1/4
Explanations:
Note: For a scale factor to cause a reduction, it must have a value less than 1.
Theree helpful points to note:
1) A scale factor of 1 will make an image equal in size to the original object/image
2) A scale facor less than 1 will cause a reduction in size
3) A scale factor more than 1 will cause an enlargement in size.
All the choices (100, 7, 4) will cause an enlargement because they are greater than 1 in value, except 1/4.
1/4 is less than 1, therefore it will cause a reduction in size.