2、(90/ 10+70/ 10)/2=8, 100/8= 12.5。

3、432/ 16=27,27-9= 18,432/ 18=24,24- 16=8

4.3 hours and 50 minutes =23/6 hours

1: 1.5=x:23/6，x=23/4，23/4*60=345

5, 38x+23y=450, x+y= 15, the solution is: x=7, y=8.

6、(2500-250)/(65+60)= 18

7. If the truck speed is X, the bus speed is 4x/5.

2x+(90/x+2)*4x/5=90, the solution is: x=5, 5*4/5=4.

8、45*2/(60-45)=6,

135/(60-45)=9

9、250/(5/2)-53=47

10、 105/(40+40*3/4)= 1.5

1 1、 12*2/( 1-9/ 10)=240,240*( 1+9/ 10)=456

12, [(s/2)/2.5]*3/5=(s/2-42)/2.5, the solution is: s=2 10.

13、900/ 150=6,( 1. 1* 1000-65*4)/6= 140, 140-65=75

Note: A travels 65 kilometers per minute, not 65 meters; Four minutes after b left, no, it was a.

14. It was found t minutes after the lost item.

V flow +(v static -v flow) *t+v flow *5=(v static +v flow) *5

t=5

I hope to do my homework by myself, but I really won't ask for it again, understand?