The second approximation number is a range value, which refers to the whole ten, whole hundred and whole thousand close to the exact number: if it is greater than 700, it can approximate 700 to the left and 800 to the right, but it cannot approximate 600 and 900. But except for more than 900 and 9000, it does not cross the highest unit, and rounding is not mentioned for the time being. The sixth question on page 98 of the textbook, 1 estimation, is about 900,900+900+900 = 2,700 (people); Within 3000, you can sit; On page 99 of the textbook, question 8, there are more than 700 omissions, which is about 700,900 omissions, which is about 900,700+900 =1600, that is, 1500. A: That's enough.