A. B is 546km away from the two places. The two buses start from the two places at the same time and meet each other in three hours. The speed of car a is three times that of car B, and car a runs every hour How many kilometers?

Car a per hour: 546 △ 3 △ 3 + 1 X3 = 136.5 (km)

Solving the system of inequalities 3 (x + 2) < x + 8. X / 2 ≤ [(x-1) / 3]

3（x+2)＜x+8 x/2≤(x-1)/3
3x+6＜x+8 3x≤2(x-1)
3x-x＜8-6 3x≤2x-2
2x＜2 3x-2x≤-2
x＜1 x≤-2
In conclusion, X ≤ - 2

On a map with a scale of 1:4000000, it is measured that a and B are 18 cm apart, and buses and vans are separated from a and B
The speed ratio of passenger car and freight car is known to be 5:4, and the speed difference between passenger car and freight car is calculated

18 cm=0.18 m
According to 1:4000000 conversion
720 km from Party A and Party B
Set the speed of passenger car as 5x and that of freight car as 4x
According to the meaning of the title
5 h*（5X+4X）= 720 km
The solution is x = 16 km / h
A: the speed difference between passenger cars and freight cars is 16 km / h

Next, vector a = (2, - 1) vector b = (3, - 4) find the membrane of vector a B and vector a B. judge that the angle between vector a and B is acute angle and obtuse angle

ab=(2,-1)(3,-4)=2*3+(-1)(-4)=10
|a|=√(2^2+1^2)=√5
|b|=√(3^2+4^2)=5
cos=ab/(|a||b|)=10/(5√5)=2√5/5>0
So the angle between a and B is acute

The Red Cross Society set up two rescue teams. The ratio of the number of the first team to the number of the second team was 5:2. According to the needs of the work, one eighth of the number of the first team was transferred to the second team. Soon after receiving the urgent task again, 14 people were transferred from the first team. At this time, the number of the two teams was equal. How many people were there in the first team?

Suppose that the original two teams had 5x and 2x people respectively
5X*(1-1/8)-14=2X+5X*1/8
35X/8-14=21X/8
7X/4=14
X=8
The first team used to be 8 * 5 = 40

At 1, 2, 3, 4 , 9991000, of these 1000 natural numbers, the total number of times the number "0" appears is______ Times

Among these 1000 natural numbers, the number "0" appears a total of 9 + 180 + 3 = 192 times

A car drove from city a to city B at a speed of 45 kilometers per hour. It took five ninths of the whole journey in three hours. How many kilometers are there between city a and city B?
The quantity relation also needs to be improved

The distance between the two cities is x km, 5x / 9 = 45 * 3x = 243 km

In the known Pentagon ABCDE, if angle B = 1 / 2, angle a, angle c = 1 / 2 (angle D + angle E), find the degree of angle B + angle C

Angle a + angle B + angle c + angle D + angle e = 540
Angle B = 1 / 2, angle a, angle c = 1 / 2 (angle D + angle E)
SO 2 angle B = angle a, 2 angle c = (angle D + angle E)
2 angle B + angle B + angle c + 2 angle c = 540
3 (angle B + angle c) = 540
Angle B + angle c = 180

A car delivers goods to the mountain area at an average speed of 42km / h and arrives in six out of seven hours. It only takes three out of four hours to return from the original road. What's the average speed?

If a is a rational number, try to compare the size of a and - A, is it a ＞ - a?

Not necessarily
a>0 -a-a
a0 a

A. B is 546km away from the two places. The two buses start from the two places at the same time and meet each other in three hours. The speed of car a is three times that of car B, and car a runs every hour How many kilometers?