The trouble is, this sort of estimation has become a part of every math problem, needlessly gumming up and dumbing down regular math instruction.
I think estimation comes naturally over time.
I suck at math but I’ve found my own means of estimating to close and measuring to accurate.
I had a job where I had to cut a hole in the center of truck lids for a key/latch assembly. Rather than measuring the whole distance and calculating the center, I measured to a round number near center and then measured the same distance from the other side and gave myself a nice short 2 to 4 inches distance to measure the center accurately. The boss shook his head at it but couldn’t complain because I was finding center.
Please check the problem in the main article once again. The problem was correctly solved at the top. Then as a check on the answer simple 100’s and tens were used. I was trained in this method 60 years ago. Scientists use it, engineers use such a check, businessmen use it. IT IS A METHOD USED TO CHECK ONES INITIAL COMPUTATION. IT IS NOT THE COMPUTATION ITSELF. IT IS NOT INTENDED TO REPLACE TRUE AND ACCURATE COMPUTATION BUT TO CHECK.