(1) selling means reducing the number of original books by 400-260 = 140 (book) and increasing by 220, that is, increasing by 140+220=360 (book), so the number of fairy tales is reduced. A few percent reduction means a few percent reduction, so 360/400× 100% is equal to 90%.

(2) "The actual investment is 5% more than planned." It can be seen from this sentence that 1 unit plans to invest. Since the actual investment is 5% more than planned, which means that the actual investment is (1+5%), the following is simple. If we know unit one, we can find out 1+5% of unit one, and multiply it by it, which is 140× (1+5%) = 65438.

(3) Because the number of boys accounts for 40% of the total number of students in the school, girls account for 60%, and girls account for 60%-40% = 20%. The number of girls is 256 more than that of boys, and this 20% is equal to 256. It is known that the first unit has 256 people in 20%. To find unit one, 256÷20%= 12809 (person) should be used.

(4)8000× 3×4.2 1%=967.2 (yuan) 967.2×5%=48.36 (yuan) 967.2-48.36 = 9 18.84 (yuan) A: Not enough.

(5)6000×3×4. 12%=75.6 (yuan) 75.6×5%=3.78 (yuan) (75.6-3.78)+6000 = (too much trouble, forget it).

This is the simplest question in grade six, and I can't guarantee that the last two questions are correct. It is too much trouble to calculate. You can calculate them with a calculator. Give points!