How to do the estimation in primary school mathematics?

For example, 2 19 is estimated to be an integer, which is 200.

247 should be 200,

When the last digit of a precise number reaches 5, it goes forward by one digit.

If you are not satisfied, give up and make up.

Estimation is an important part of computing power.

Estimation method

1. Rounding

Example: arithmetic square root of 2 (reserved as 0.0 1)

Solution: Root number 2 =1.414 ≈1.41.

Step 2: Step 1.

For example: How many are four pens in 2.6 yuan (to the whole number)?

Solution: 2.6*4= 10.4 yuan ≈ 1 1 yuan.

If rounded, it is 10 yuan. If it is not enough, you should go up.

3. Tailing method

Example: If you buy a pen from 20 yuan and 3 yuan, how many pens can you sell?

Solution: 20/3=6.6666...6 branches.

If rounded, it's seven. If you can't buy it, you have to sell it.