Estimation in maths is not just about rounding up or down numbers.
It called for logically thinking and is done on a case-by-case basis.
Take for example, 302 x 11.
What is the estimated product of the 2 numbers?
We can choose for it to be 300 x 10, which gives 3000.
But how about being more accurate in our estimation?
300 x 11 gives 3300 !
We can use "11" instead of closing in to "10" of the first instance.
Logical thinking at play here...
But why choose "11" instead of the "10"?
The answer is simple.
Since the first number is 300, multiplying it with "11" is still within any person's ability. Therefore using "11" as part of the estimation is closer to the actual answer.
Now, how about 314 x 11?
Here, the answer estimated will be 310 x 10 = 3100, to be practical.
310 x 11 will be harder to estimate. Therefore "10" is chosen in preference to "11" as in the case of the previous example. (We are not talking about mental maths, but maths for "normal" people.)
Estimation, thus, calls for a fast but accurate production of numerical answer. It involves thinking and choosing numbers that are easy to handle.
Estimating answers can be fun as shown. It can be a challenging game where students aim to be first to give the most accurate answer.
Have fun estimating! :-) It gets more interesting as you go on.....