4 / 5 of a is equal to 2 / 3 of B, and a is a fraction of B

4 / 5 of a is equal to 2 / 3 of B, and a is a fraction of B

The number a is the number B
=2 / 3 ／ 4 / 5
=10 out of 12
=5 out of 6

How many natural numbers less than 1000 can be made up of numbers 0-5?
A236 B111 C131

Have you ever learned permutation? It's very easy to use
The process is not easy to write, because there are signs. It is not easy to express
Let me write it briefly
One: there are six
2 digits: 6 * 5-5 = 25
3 digits: 6 * 5 * 4-5 * 4 = 100
131 in total

The original plan is to travel 45 kilometers per hour, and the actual speed has been increased by 1 / 3
And arrive 2 hours ahead of schedule!

2 × 45 = 90 45 × one third = 15 90 △ 15 = 6 [6 + 2] × 45 = 360

As shown in the figure, BD and CE are the heights of △ ABC

Prove: as shown in the figure, take the midpoint F of BC, connect DF, EF. ∵ BD, CE is the height of △ ABC, ∵ BCD and △ BCE are right triangles. ∵ DF, EF are the middle line on the hypotenuse of RT △ BCD and RT △ BCE respectively, ∵ DF = EF = BF = CF. ∵ e, B, C, D are on the circle with F as the center and 12bc as the radius

The two vehicles run towards each other at the same time at a distance of 100km, and then turn back when they reach the starting point of each other,
How many hours does it take for the two cars from departure to the third meeting?

The third meeting was five whole courses
So it takes 100 × 5 (40 + 60) = 5 hours

Given a & sup2; - 2A + B & sup2; + 6B + 10 = 0, then the value of 1 / (1 / A + 1 / b) is

a²-2a+b²+6b+10=0
a²-2a+1+b²+6b+9=0
(a-1)²+(b+3)²=0
a-1=0 b+3=0
a=1 b=-3
1/(1/a+1/b)
=ab/(a+b)
=1*(-3)/(1-3)
=3 / 2 (3 / 2)

A fast train is 70 meters long and a slow train is 90 meters long. If two trains are running in the same direction, it takes 20 seconds for the fast train to catch up with the slow train and leave the slow train completely. If two trains are running in opposite directions, it takes 4 seconds for the two trains to meet and leave. How many kilometers do they travel per hour,

Let the speed of the fast train be x m / s and that of the slow train be y m / s
20x－20y＝70＋90
4x＋4y＝70＋90
The solution is: x = 24
y＝16
Speed of express train: 24m / S = 86.4km/h;
Speed of local train: 16m / S = 57.6km/h

Curve polar coordinate equation P = 1 is transformed into rectangular coordinate equation

Square
P²=1
Then x & sup2; + Y & sup2; = 1

There is a pile of sand on the construction site. 40% of the sand is used in the first day, and 10.8 tons are used in the second day. 62.5% of the sand is used in two times. How many tons of sand is used in the first day?

8 (62.5% - 40%) = 10.8 △ 22.5% = 48 tons a: the original sand is 48 tons

(2011. Jiading District three mode) known M is a point in Delta ABC, and AB - AC=23, BAC=30 BAC=30, if Delta MBC, Delta MCA and delta MAB are 12, x, y, the minimum value of 1x+4y is ()
A. 20B. 18C. 16D. 9

It is known that ab · AC = bccos ∠ BAC = 23 {BC = 4, so s △ ABC = x + y + 12 = 12bcsina = 1 {x + y = 12, and 1x + 4Y = 2 (1x + 4Y) × (x + y) = 2 (5 + YX + 4xy) ≥ 2 (5 + 2yx × 4xy) = 18, so B