Car a and car B start from two places 298 kilometers apart. Car a is five times faster than car B by 20 kilometers per hour. They meet 30 minutes later Q: what's the speed of the two cars

Car a and car B start from two places 298 kilometers apart. Car a is five times faster than car B by 20 kilometers per hour. They meet 30 minutes later Q: what's the speed of the two cars

Let the speed of car B be x km / h
5x+20+x=298÷1/2
6x=576
X = 96 (km / h)
Then the speed of car a is 96 × 5 + 20 = 500 (km / h)

Simplify the evaluation of 3a-abc-3c & # 178; - 3A + 3C & # 178; - 3A + 3C & # 178; - 2abc-a, where a = - 6 / 1b = 2 C = - 3
Format:
Copy the title and draw the same items,
=…………
=…………
When a = - 1 / 6, B = 2, C = - 3
Original =
=……

3a-abc-c²/3-3a+c²/3-3a+c²/3-2abc-a
=(3a-3a-3a-a) + (- abc-2abc) + (- C & # 178 / 3 + C & # 178 / 3 + C & # 178 / 3) the same items are in brackets
=-4a-3abc+c²/3
When a = - 1 / 6, B = 2, C = - 3
The original formula = - 4 * (- 1 / 6) - 3 (- 1 / 6) * 2 * (- 3) + (- 3) & # / 3
=2/3-3+3
=2/3

Party A and Party B start from the same place in the opposite direction at the same time. Party A travels 12 kilometers per hour by bicycle and Party B 40 kilometers per hour by motorcycle
(1) Party A and Party B start from the same place in the opposite direction at the same time. Party A travels 12 kilometers per hour by bike; Party B travels 40 kilometers per hour by motorcycle. After three-quarters of an hour, the distance between them is () kilometers

40×3/4+12×3/4
=30+9
=39 (km)
or
（12+40）×3/4
=52×3/4
=39 (km)

Finding the general solution of the differential equation y '- 2Y = e ^ x

The general solution of Y & # 39; - 2Y = 0
r-2=0
r=2
General solution y = C1E ^ 2x
A special solution y to the original equation*
Let y * = AE ^ X
y*'=ae^x
ae^x-2ae^x=e^x
-a=1
a=-1
That is y * = - e ^ X
therefore
The general solution is y = C1E ^ (2x) - e ^ X

A middle school organized some seventh grade students to experience the natural life in the "nantianhu scenic spot". The scenic spot was allocated to several dormitories of the school. If there were 8 students in each dorm, there would be 12 beds less; if there were 10 students in each dorm, there would be one spare room. How many dormitories did the scenic spot give? How many students participated in the activity?

There are x dormitories
8x+12=10（x-1）
x=11,
Number of people = 10 × (11-1) = 100

Let K be an integer and the solution X of the equation KX = 4-x be a natural number
Such as the problem, requirements: before each step to write shift, merge similar and so on

kx=4-x
kx+x=4
x=4/(k+1)
Because x is a natural number, that is, x = 1,2,3
When equal to 1, k = 3
When it is equal to 2, k = 1
When it is equal to 3, there is no solution
When it is equal to 4, k = 0

The total weight of the two barrels of oil is 90 kg. If 25% of the oil in barrel a is poured into barrel B, the weight of barrel a is half that of barrel B
Q: how many kilos did a and B each weigh?

If 25% of a barrel oil is poured into B barrel, the weight of a barrel oil is half of B barrel oil
The weight of B is:
90÷(1+1/2)
=90x2/3
=60 (kg)
Therefore, kedejia originally had:
(90-60)÷(1-25%)
=30÷75%
=40 (kg)
B: originally, there are:
90-40 = 50 (kg)

The quadratic function y = x + MX + N, if M-N = 0, then its image must pass through a (- 1,1) B (1, - 1) C (- 1, - 1) d (1,1)

A

There are 20 boys and 30 girls in the school dance team. The ratio of boys to girls is () the number of boys is () the number of girls is ()
The school dance team has 20 boys and 30 girls
The ratio of boys to girls is () the ratio of boys to girls is () the ratio of boys to girls is (), the ratio of girls to boys is (), the ratio of girls to boys is () the ratio of girls to boys is () ()
The ratio of the number of male students to the total number of dance team is (), male students account for () of the total number, female students account for () of the total number
Mr. Zhang raised a group of ducks and geese. Among them, there are 400 ducks. The ratio of ducks to geese is 5:3. How many geese are there?

There are 20 boys and 30 girls in the school dance team. The ratio of boys to girls is (2:3) and the ratio is (2 / 3). The number of boys is (2 / 3) of girls. The ratio of girls to boys is (3:2). The number of girls is (3 / 3) of boys

If ABC = 1, a + B + C = 2, A2 + B2 + C2 = 3, then the value of 1ab + C − 1 + 1BC + a − 1 + 1ca + B − 1 is ()
A. -1B. −12C. 2D. −23

From a + B + C = 2, the square of both sides, A2 + B2 + C2 + 2Ab + 2BC + 2Ac = 4, substituting the known into, AB + BC + AC = 12; from a + B + C = 2, C-1 = 1-a-b, AB + C-1 = AB + 1-a-b = (A-1) (B-1), similarly, BC + A-1 = (B-1) (C-1), Ca + B-1 = (C-1) (A-1), the original formula = 1 (a − 1)