13, condition unknown.
14,27 ÷ (5+4) = 27 ÷ 9 = 3 (hours), teacher distance: 14×3=42 (kilometers).
15,130g of saline water with 5% salt and 9% salt were mixed to make saline water with 6.4% salt. Then, how many grams of salt water with a salt content of 6.4%?
Solution: Suppose there is X kilograms of salt water with a salt content of 9%.
130×5%+9% x =( 130+x)×6.4%
6.5+0.09x=8.32+0.064x
0.026x= 1.82
X=70
70+ 130=200 kg
16. When Party A completes 2/5 of the whole journey, Party B completes 2/5× 8/11=16/55; 9.6 ÷16/55 = 33km
17,2 ÷ 0.5 = 4 (segment) 4- 1=3 (times) 24÷3=8 minutes/time; 2÷0.4=5 (segment) 5- 1=4 (times) 8×4=32 (minutes)
18. Assuming that both the train ticket and the boat ticket are110, then the travel expense is 250× (1+110) = 275 yuan, which is 280-275 yuan. Air ticket before departure: 5 ÷ (1/5-110) = 50 yuan; Return train ticket: (250-50) × (1+110) = 220 yuan.
19, the answer is 40×( 1- 10%)+4=40 (person); 40÷80%=50 (person)
20. The number of people in the first workshop accounts for 20% of the total number of people in the third workshop, and the number of people in the second and third workshops accounts for1-20% = 80%; The number of two workshops is 2/3 of that of three workshops, and the second workshop accounts for 80%×2/(2+3)=80%×2/5=32% of the total number of three workshops. 30÷(32%-20%)=250
2 1, 160 ÷ ( 1- 1/3) × 5/6- 1/3 = 160 ÷ 5/9- 1/3
22, 42 ÷ ( 1- 1/3) × 4/(3+4)- 1/3 = 42 ÷ 1/2 1.
23700× (1-4/7) = 700× 3/7 = 300 (kg); 300( 1-5/8)= 800 (kg)
24. Hypothetical method: assume that both Party A and Party B do 3/4; Then Party A * * * makes 184×3/4= 138 (pieces); Suppose it is more than the actual situation138-123 =15 (pieces); If 5/8 made by A is taken as 3/4, then 3/4-5/8 =1/8 of A is calculated;
A yes; 15 1/8 = 120; Party B: 184- 120=64 (pieces)
25，4 1÷( 1-3/4)= 164m； ( 164+ 16)÷( 1-2/5)= 300m。
26、4/7-3/7×( 1+20%)×{3/7÷[4/7×( 1- 10%)]}= 1/7; 17/1/7 =119 km
27. According to the number of volleyball ×( 1- 1/3)= the number of football ×( 1-3/5), the number of volleyball is 2/5/2/3 = 3/5 of the number of football; Number of football: 48 ÷ (1+3/5) = 48 ÷ 8/5 = 30; Number of football: 30×3/5= 18.
28. Total tonnage of pile A and pile B:10× (3/5-2/5) = 20 ÷1/5 = 50 tons; A: 50×2/5=20 tons; B: 50×3/5=30 tons.
29, from 48: 42 to 8: 7; 7/20÷7/ 15=3/4; 8/ 15×3/4=2/5; 1/2-2/5= 1/ 10; 24 ?110 = 240km.
30、80×2÷( 1- 1/5)= 160÷4/5 = 200km。
3 1，24÷(3/5×2- 1)= 24÷ 1/5 = 120km。
32. It is known that the speed ratio of car A and car B is 3: 4 and the distance ratio of car A and car B is 3: 4; 30÷[3/(3+4)-2/5]= 30÷[3/7-2/5]= 30÷ 1/ 15 = 450km。