Analysis: the area of a rectangle = length× width, so the length is reduced by 5 times and the width is expanded by 5 times, which has no effect on the area, and it is still 625. At this time, the figure becomes a square, so it can be seen that the side length of the square × side length = 625.

The decomposition of 625 indicates that 625 = 5× 5× 5 indicates the side length of a square, so it should be 25.

That is, the original width is 25 ÷ 5 = 5, (because the width has been expanded by 5 times to 25, it will be divided by 5 when it is restored).

Similarly, the length is 25× 5 = 125.

This kind of problem is actually a little sensitive to numbers, which can be seen at once. If you really can't see it, decompose 625 and observe it again. The side length is divided into 5×5 and 5×5, that is, 25 (this step is the key! ! ).

I hope this analysis can help you, and I hope you can master it and turn it into your own knowledge. You will do it next time! !