Estimation method:
Rounding: 0, 1, 2, 3, 4, no carry, 5, 6, 7, 8, 9, carry.
For example:
A set of tickets and tickets 49 yuan, the fourth grade needs a 104 set of tickets, how much do you need to prepare?
Method 1: 49× 104≈5000 (yuan) 50* 100.
Method 2: 49× 104≈5500 (yuan) 50 * 1 10.
Method 3: 49× 104≈5250 (yuan) 50 * 105.
The first estimation method is very convenient, because 49 is regarded as 50, 104 is regarded as 100, and 50× 100 equals 5000.
In the second estimation method, because 49 is regarded as 50, and 104 is regarded as 1 10, the estimated result of 50×10 is equal to 5500, which is definitely greater than 49× 104.
In the third estimation method, because 49 is regarded as 50 and 104 as 105, both numbers are a little too big, so the estimation result of 50× 105 is equal to 5250, which is very close to the exact value.