323÷4≈; 359÷6≈; 103÷2≈490÷5≈; 2 10÷5≈; 432÷7≈; 86÷4≈; 274÷9≈48×72≈; 29×80≈。
Equal to material oral calculation:
About equal means about how much, which is an estimate, calculated according to the rounding algorithm. Usually tell the exact number of digits. If it is accurate to ten digits, according to the rounding algorithm, 49 1 is approximately equal to 490.
Rounding is an accurate counting reservation method, which is essentially the same as other methods. But the special point is that the difference between the reserved part and the actual value cannot exceed half of the last order of magnitude: if there is a probability of 0 ~ 9, the error sum of this method is the smallest for a large number of reserved data. This is why we use this method as the basic booking method.