A few contest questions, please help me

1、x÷3=(170-x)÷4+10

Solution x 3 170 4-1 4x+10

x÷3＝1/3x+1/4x＝

7/12x＝

x x 902, A, B ergonomics and: 1 18

Let's say A is dry for 4 days: 1 18 4 2 9

A ergonomics: 2 9-1 5 1 45

B Efficacy: (2 9-1 45 3) 4 7 180 A: 1 1 45 45 days.

B: 1 7 180 25 and 5 7 days.

3. The circumference of the semicircle 2r+r faction (2+faction) r(2+r

4 4 square centimeters.

4. Set up x kg of original salt water.

10％x+（x+8）×8％】÷x+8）＝8％1/10x+2/25x+16/25＝2/25×（x+8）9/50x+16/25＝2/25x+16/25x＝9/50×2/25

x9/625

25 (1+40) RMB.

1200 RMB.

1200 RMB.

420 (1+86) RMB.

Yuan. Yuan. Yuan. Fold.

What the hell?

Elementary school is actually in the question!!

First of all, the presence of k in liquid ammonia is not elemental, so c is incorrect, and it cannot be explained by physical properties in chemical reactions.

And A, if it is a comparison of elemental matter, is correct, but not here, because be exists in elemental matter, and k is not. It should be said here that be is more prone to losing electrons than k.

It's hard to say that A is wrong, but B is clearly right in comparison. c is definitely not right, because the solvent of the reaction is liquid ammonia, which is at a low temperature, and be and k are solids, which has nothing to do with the boiling point. Only such a reaction as KCl+NaCl+K at high temperature can be explained by the low boiling point of K, because at this point K is already vaporized.

Since BE(NH2)2 is insoluble enough, the degree of positive reaction of BE+2NH3 BE(NH2)2+H2 in thermodynamic analysis must be greater than that of 2K+2NH3 2KNH2+H2, which indicates that BE is more active than K in liquid ammonia, which is valid. So A is actually correct.

Be livelier than K, and be wrong at all times; The boiling point of be is higher than the boiling point of k, if there is after k, it may be true, now there is not, liquid ammonia, the temperature should be very low, so false; A reaction that cannot generally occur occurs under certain conditions, and it must be under this condition that at least one product can be separated from the reaction system, either precipitated or gas, etc., and now there is no behind BE(NH2), probably because KNH2 is not soluble in liquid ammonia.

A, B, and C each have **x, y, and z.

1;A sends x B first, and x C gives B and C respectively: x B = y, x C = z2; B then sends Y A, Y C to A and C, Y A = x-x B - x C, Y C = x C + z3; C then sends Z A, Z B to A and B, Z A = 2y A, z B = 2y C Finally, we can know: A 3 = 4 (x-y-z) = 32

B3 = 2 (3y-x-z) = 32

C3 = 7z-x-y = 32

x=52y=28

z=16

First, rotate the triangle ABC 180 degrees according to point D to obtain the parallelogram ABCC2, as shown in the following figure

ac2‖bc

BCC2= AC2C, CC2B= ACC2 and CD are the angular bisectors of ABC.

acc2=∠bcc2

ac2c=∠acc2

The triangle acc2 is an isosceles triangle and AD is the bisector of the C2AC angle.

ac2=ac

i.e. bc=ac

The same is true for ad=db: in the triangle a1b1c1, a1d1=a1b1a1d1=ad

a1d1c1= adc, cd=c1d1 adc a1d1c1

ac=a1c1, ∠a=∠a1

and ab=a1b1

abc≌△a1b1c1

Haha, it's finally out. There may be an easier way.

You should understand it.

In the first five cases, four students A, B, C, D(1) 21,21,—21,—21;(2) 7，7，—7，—7；(3)21，—7，—7，—7；(4)—21，7，7，7；(5)21，7，—21，—7。(1) When student A has 21, -21 two kinds, and there are 21 and -21 kinds of classification for B (the data is not explained later, the data is not large, and it can be easily analyzed with a tree diagram, so there is no need to arrange and combine here), and it is easy to calculate six kinds, and (2) the same six kinds. Similarly, (3) Student A has two kinds of 21 and -7, which is easy to calculate by the tree diagram method is one at 21 and three at -7, a total of four types.

4) Same as (3) four kinds. (5) is a simple permutation and combination, A four, B three, C two, 4 times 3 times 2 to get 24 kinds. Six plus six plus four plus four plus twenty-four get forty-four, and the proof is completed.

Oil 1 3 is 42-29 = 13 kg.

Barrel weight 42-13 (1 3) = 3 kg.

See Diagram Stove Shelter. Yinhong Prefecture is absolutely stunted.