The two passenger and freight cars leave from a and B at the same time. When they meet, the distance ratio of passenger and freight cars is 4:5 After the meeting, the freight car traveled 27 kilometers per hour more than before, and the passenger car still drove at the original speed, and finally arrived at the same time. It is known that the passenger car traveled for 10 hours, and the distance between a and B is calculated Ask to write the process, not too complicated and explain

The two passenger and freight cars leave from a and B at the same time. When they meet, the distance ratio of passenger and freight cars is 4:5 After the meeting, the freight car traveled 27 kilometers per hour more than before, and the passenger car still drove at the original speed, and finally arrived at the same time. It is known that the passenger car traveled for 10 hours, and the distance between a and B is calculated Ask to write the process, not too complicated and explain

The distance ratio is 4:5
Speed ratio = 4:5
Finally, they arrived at the same time
The velocity ratio becomes = 5:4
Trucks travel 27 kilometers more per hour than before
If the speed of freight car is 4a, the speed of passenger car is 5A
(4a+27)/(5a)=5/4
a=12
Bus speed = 5A = 60
Distance between a and B = 60 * 10 = 600 km

If the common ratio of the equal ratio sequence {an} is Q, then "Q ＞ 1" is a ()
A. Sufficient and unnecessary condition B. necessary and insufficient condition C. sufficient and necessary condition D. neither sufficient nor necessary condition

When A1 ＜ 0, neither the condition nor the conclusion can be deduced from one party. As shown in Figure 1, it is the case of A1 ＜ 0, Q ＞ 1, but the sequence decreases; as shown in Figure 2, it is the case of 0 ＜ Q ＜ 1, because A1 ＜ 0, it is the case of increasing sequence. So D is selected

There are 120 people in team a, 35 people in team B and 23 people in team C. how many people are there in team B?

120 × 23 × 35 = 80 × 35 = 48 A: Team B has 48 people

40 is less than 50 ()%, () is more than 80 by 12.5%, and 30 is more than () by 25%
(2) There are 50 students in a class. One of them failed in the final math test. The pass rate of this test is ()%
(3) A color TV set is sold at 75% discount, which regards () as unit "1", and the current price is ()% of the original price
(4) 50 kg increases by 20% and then decreases by 40% to 12 km
(5) The original price of a dress was 150 yuan, but now it's 90 yuan. This dress is sold at a discount of (), and the price is reduced by ()%

40 is less than 50 (20)%, (90) is more than 80 (12.5%), and 30 is more than 24 (25%) (2) there are 50 students in a class, and one of them failed in the final math test. The pass rate of this test is (98)%
(3) A color TV set is sold at 75% discount, which regards (original price) as unit "1". The current price is (95%) of the original price
(4) 50 kg increases by 20% and then (60) kg. (20) km decreases by 40% to 12 km
(5) The original price of a dress is 150 yuan, now 90 yuan. This dress is sold at a discount of (6%), and the price has been reduced by (40)%. If you don't understand, please ask. If you have any help, please adopt it. Thank you!

A and B trains leave from both places at the same time. Train a runs 50 kilometers per hour, while train B runs 60 kilometers per hour. When the two trains meet, train a runs 300 kilometers. How many kilometers are there between the two places?

Speed ratio of vehicle a to vehicle B = distance ratio
Driving distance of vehicle B / 300 = 60 / 50
One car driving distance = 300 * 60 / 50 = 360 km
Distance between the two places = 300 + 360 = 660 km

As shown in the figure, in the triangle ABC, ad be is a triangle with two middle lines to find s edc:s Triangle ABC

In △ ABC, ad and be are two median lines, and De is the median line of △ ABC, then de ‖ AB and de = AB are obtained. Then △ EDC ∽ ABC is proved, and the answer is obtained by the area ratio of similar triangle equal to the square of similar ratio
∵ in △ ABC, ad and be are two midlines,
∴DE∥AB,DE=AB,
∴△EDC∽△ABC,
∴S△EDC：S△ABC=（）2=1：4．
So choose B

The distance between the two cities is 870 km. A freight train runs 55 km per hour from city a to city B at 6 a.m. and a bus from city B to city a at 8 a.m
The average speed is 9 / 11 of a freight car. How many hours after the freight car leaves, is it 60 kilometers away from the passenger car?

(870-55 × 2-60) / (55 + 55 × 9 / 11) + 2 = 9 hours

By observing the following formulas: 1 ^ 2 + 1 = 1x2, 2 ^ 2 + 2 = 2x3, 3 ^ 3 + 3 = 3x4 And conjecture the following rule (expressed by natural number n)

n^n+n=nx(n+1)
And your formula 1 ^ 2 + 1 = 1x2 is wrong. It should be 1 ^ 1 + 1 = 1x2

The highway between a and B is 375 kilometers long. A car leaves from a place, and the first two hours is 150 kilometers. According to this speed, it will take several hours
There are 18 girls in the science and technology group of the school. The number of boys is two times less than that of girls. How many students are there in the science and technology group of the school? (formula)

(375-150) / (150 / 2) = 3 hours
18+（18*2-2）=52

Find the value range of real number m respectively, so that the equation x ^ 2 + 2x + m + 1 = 0 (1) has two negative roots (2) and exactly one root in the interval (0,1)
Find the value range of real number m respectively, so that the equation x ^ 2 + 2x + m + 1 = 0 (1) has two negative roots (2) has exactly one root in the interval (0,1), and (3) has two real roots, which are larger than - 2

The axis of symmetry is x = - 1
Let f (x) = x ^ 2 + 2x + m + 1
1 has two negative roots if and only if f (0) > 0, the discriminant > = 0, so - 1