Analysis: 1. Winding with double folding rope for two weeks, leaving 1.5 meters, that is, winding without discount for 2×2 weeks, leaving 1.5×2 meters. Measured with a three-fold rope, it winds more than 2 meters a week, that is, it winds 1×3 times without discount, leaving 2×3 meters. Take (2×3 m-1.5×2 m) as the length of (about 2×2 weeks-1×3 weeks).

2. Divide the total scores of Chinese, Mathematics and English into 4 parts on average, and take 1 part plus 4.5, which is equivalent to 3/4 of the sports scores. Or: let's set the sports score to x and get it.

x-(84×3+x)÷4=4.5

x-(84×3+x)× 1/4=4.5

x-(84×3)×4- 1/4x=4.5

x- 1/4x=4.5+(84×3)

( 1- 1/4)x=4.5+(84×3)

x =[4.5+(84×3)]⊙( 1- 1/4)

3. The round trip 1 hour can drive 30× (1+4/5) kilometers, and the round trip 1 hour can drive 12 ÷ 2 30×( 1+4/5) kilometers. Divide this distance by 2, which is the maximum distance a ship can sail.

4. The ratio of the length of the repaired and unrepaired parts is 1: 3, that is, the repaired part accounts for1/(1+3) of the whole process; The length ratio of repaired and unrepaired is 1: 2, that is, repaired accounts for 1/( 1+2) of the whole process. 300m covers the whole journey1(1+2)-1/(1+3). 300÷1/(1+2)-1/(1+3) is the result.

5. When you run forward, you are chasing time = distance ÷ speed difference. Speed difference = teacher speed-team speed, when running backwards, it is a problem of meeting cars. Meeting time = the sum of distance/speed. Speed sum = teacher speed+team speed. The distance is 450 meters. Twice adds up to what you want.

6. When the number of books exceeding 10 is X, bookstores A and B spend the same amount of money. get

10+75%x=( 10+x)×85%

x= 15

Money spent (10+15) ×10 = 250 (yuan)

When there are less than 25 books or less than 250 yuan, Bookstore B saves money than Bookstore A ... When there are more than 25 books or books above 250 yuan, Bookstore A saves money than Bookstore B. When Mr. Zhang wants to buy 20 books, it is cheaper to buy them at Bookstore B. 250 yuan can buy 25 books.

7. If it is all done by Party A, it takes Party A1-120 days to complete 14 days, and the rest is that Party A is slower than Party B, divided by their poor efficiency, which is the number of days that Party B has done. It is equivalent to the problem of chickens and rabbits in the same cage.

The number of days in A is14-(1-14/20) ÷ (112-120) = 5 (days).

8. Suppose that in X years, my father will be six times as old as Xiao Ming.

(5+x)×6 =5×7+x

x= 1

9、

10, the speed ratio of Party A and Party B is 5: 4, that is, the distance ratio of Party A and Party B after meeting is 4: 5, the speed ratio of Party A and Party B after meeting is 5× (1+20%): 4× (1+25%), and the time ratio of reaching the destination after meeting is 4 ÷ 5×. 1-4 ÷ 5× (1+20%): 5 ÷ 4× (1+25%), that is, the share of 15 km. Calculate the distance of the second line after meeting and divide it by 5/(4

Solution:15 ÷ {1-4 ÷ 5× (1+20%)/5 ÷ 4× (1+25%)} ÷ 5/(4+)

=8 1 (km)