1、⑴X=- 17/5、⑵X=-24/5、⑶X=3/5

2、⑴X=5/4，⑵X=- 12/5

3、X =-4x & gt； -4 X & lt； -4 X & lt； -8/3

5、X=-6.4Y=- 15

6、⑴X= 1，Y= 1，⑵X= 16/5，Y=2/5

7、0.5t≥6，t≥ 12，0.5t≤8.5，t≤ 17

8、Y = 2.4(0 & lt； X≤3)，Y = X-0.6(X & gt； 3, and x is an integer)

9. When spending 0.8 yuan in Mall A, the consumption is X yuan (0≤X≤200) or 200+0.7 (X-200) = 0.7x+60 (X >; 200)

Then compare

10、⑴Y=5X(0≤X≤4)

⑵Y = 5/4X+ 15(4 & lt； X≤ 12)

(3) From Y=5X, it can be seen that the influent is 5 liters per minute, and the ratio is 5-(5/4× 5+15-20) = 15/4, and the effluent is 5 liters per minute15/4.

1 1, let x seconds be the time to run at a constant speed.

Xiao Ming's distance: L=ax+ 1600, Xiao Gang's distance l=bx+ 1450.

Available equations:

100 a+ 1600 = 100 b+ 1450

300 a+ 1600 = 200b+ 1450

The whole cross-country run is in 2050.