For example: telephone 98 yuan, rice cooker 192 yuan, bicycle 403 yuan, electric fan 105 yuan. How much does it cost to buy a telephone and a rice cooker? 98 yuan is close to 100 yuan, and 192 yuan is close to 200 yuan, so 100+200=300 yuan needs 300 yuan.

1. truncation method: that is, the mantissa of each number is removed and the integer is calculated. A travel agency organized several tour groups: Lijiang 524, Huangshan 208, Great Wall 602, Jiuzhaigou 365,438+00 and Emei Mountain 265,438+09. How many people does this travel agency expect to receive?

Remove the mantissa, and add the integer hundreds to get 524+208+602+310+219 ≈ 500+200+600+300+20 =1800 (person).

2. One method: that is, the highest digit of each number is added with 1, and the integer of ten is taken for calculation. For example:

28+ 15+7+24≈30+20+ 10+30=90。

3. Rounding method: that is, mantissa is less than or equal to 4 and mantissa is greater than or equal to 5, and it is calculated by taking integer 10 or integer 100. For example, apples are 4.20 yuan per catty, so how much should 1.8 catty apples pay? The estimated value is 4.2× 1.8≈4×2=8 (yuan).

4. Ten-complement method: add the relevant figures together, which is close to 10. Such as17+8+12+24 = (17+12)+(8+24) ≈ 30+30 = 60.

5. Find the whole by parts: divide a large whole into several parts on average, and find an integer according to the number of parts. For example, to estimate the number of spectators in a stadium, first divide each stand into several parts, count the number of people in one part, then estimate the number of people in one stand, and finally calculate the number of people in the whole stadium according to the number of people in the stands.

6. According to the nature of operation, such as 457+245- 178=444, if the subtracted number is less than the added number, then the result should be greater than the original number, so it can be judged that 444 is wrong.