8/15 (1/5-115) = 4 minutes.

2.a do it every day (1-12/30)/45 =1/75.

A It takes 75 days.

B do1/30-1/75 =1/50 every day.

B it takes 50 days.

3. The armor was repaired for x days.

X * 1/20+( 14-X)* 1/ 12 = 1

X=5

4. suppose the distance is x meters and it takes t to meet for the first time.

B speed 1, A speed 4/5.

( 1+4/5)t=X t=5/9X

It takes 4/5t for B to reach A and 5/4t for A..

(5/4-4/5)t*4/3= 1/3X

t2=2/3X/( 1+4/3)=2/7X

4/3*2/7X=8/2 1X

(8/2 1+ 1/3-4/9)X=34

X = 126 km

Let Party A practice X, Party B practice Y and Party C practice Z every day.

X+Y = 1/6Y+Z = 1/4 X+Z = 1/8

X= 1/48 Y=7/48 Z=5/48

That is, Party A has 48 days, Party B has 7 days and Party C has 10 days.

6. Armor x tons per day

0.4X* 14=484-64

X = 75 tons

1. There are x people in the first workshop.

X+X+2 1+0.875(X+2 1)= 4X

X = 35 people

2. Because the distance between the post office and the station is 1/9.

So the whole journey: 0.42/(1/3-1/9) =1.89 km.

3. Set an X yuan

A = B = X，C = 3x

X+30000=3X+6000

X = 12000 yuan

4. let a have x liters and b have y liters.

(0.7X-0.6Y)/(X+Y)=0.66

{ 0.7(X-5)+0.6(Y-5)}/(X+Y- 10)= 0.6625

X+Y=50 X=30 liters, y = 20 liters.