A square has four sides and the area is 10,000 m^2. Area is determined by multiplying two sides. In this case, you can divide by two to get 5000, then again by 2 to get 2500. Each side/dimensions are 2500m^2
Estimation is a mental process of coming up with an answer that is relatively close, to allow decisions to be made. The types of estimation are quantity, computation and measurement.
An estimation strategy is simply coming up with a good estimate based on evidence and already known facts. Coming to a conclusion as close to the real answer as you can. It can also be called an educated guess.