Junior 2 math problem solving, junior 2 math problem solving

There is it if I purchase it by the first way.

y1=10×25+5×（x-10）

250+5x-50

5x+200

If I purchase it in the second way, there is.

y2=(10×25+5x)×90%

So 5x+200-(225+.)

You can know after discussing the size with 0.

When x 50, the second method is cost-effective, when x = 50, both methods cost the same amount of money, and when x is 50, the first way is more cost-effective.

Set the number of calligraphy books x, the number of brushes is y, and the cost is z(x>=10)

then the cost is: z = 25y (y>=x).

z = 25y + 5(x-y) = 20y + 5x (y=x, if 25y > i.e., y> then the second option is used.

If 25y < i.e., x<= y <, then the first option is used.

When + i.e., y< then the second option is used.

If 20y + 5x < i.e., y=or the two schemes are the same.

The first, because if = 10 then the first one saves money over the second.

MP nq is the perpendicular bisector of AB, AC.

bap=∠abp

caq=∠qac

paq= bac- bap- caq= bac- abp- qac, while abp+ qac=180°- bac (triangle inner angle and 180°), so paq= bac- (180°- bac)=220-180=40°

Connect PA and QA, because PM bisects AB perpendicularly and QN bisects AC perpendicularly, so ABP and AQC are isosceles triangles, so PBA is equal to PAB and QAC is equal to QCA, so Paq BAC ( BAP QAC) BAC ( CBA BCA) BAC (180 BAC) 40

paq＝40º

Bisector vertically isosceles triangle.

b=∠bap，∠c=∠caq

b+∠c=180-110=70°

paq=110-70=40°

2.(3,2)

Numerous strips or 8cm

median) 6The intersection of the three perpendicular lines.

First read the question clearly, and then analyze, the difficulty of this question is that it is easy to distinguish a few points clearly.

First of all, it is necessary to know the trajectory of point P, which moves in the direction of o with a uniform speed in the oABCD pentagon. Let the p point walk around the graph, and it can be seen that the three points p, o, and d are all triangles except for the same straight line, and they are triangles with od as the bottom edge. From the formula of the triangle we can know that the base edge is 2 high, the base edge is fixed and only the height changes the size of the area in motion.

2. In Figure 1, p, o, d are in the same straight line at the time of Figure 2 and the area of these 3 points is 0That is, the OE segment. Fig.1 When point p is from o to a, the area of figure 2 is from e to f.

The coordinates of point A can be obtained from point 2f in Figure 2. Figure 1 P movement on AB is the Fg segment of Figure 2. Figure 1: When point P moves on BC, the area is not marginal because the height does not change.

Look at Figure 2gh. The last segment is Figure 1P on CD, Figure 2 is the HI segment.

To sum up, the change in Figure 1 is actually the change in the height of the triangle, which corresponds to the change in the area of the triangle in Figure 2. Hope it helps you understand.

Point P starts from point D, and moves at a uniform speed along the edge of the pentagon OABCD Figure 1 starts from D and goes to O The area of PDO is 0, so Figure 2 O to E is flatFigure 1 The area from O to A is getting larger and larger, so Figure 2 E starts to go up, because the law of finding the area from O to A is different from that of finding the area from A to B, so EF is not a straight line.

Fig. 1 The area from B to C has not changed, so Figure 2 G to H is a straight lineFigure 1 The area from C to D is getting smaller and smaller, but the law of finding the area has not changed, and Hi is a straight line downward.

The main thing is that I don't understand what step I don't understand, or I don't understand it very well.

It takes 80 hours to complete by one person. Now the plan is to have some people do it for 2 hours at first, and then add 5 people to do 8 hours to complete 3 4How can Yan'an send a specific number of people involved in compiling the data?

Let's start with x people.

2x+8x+5*8=80*3/4

10x=60-40=20

x=2A: 2 people were sent at the beginning.

There is a flock of pigeons and some cages, if there are no 6 pigeons, the remaining 3 pigeons do not have a cage; If there are 5 pigeons flying back, together with the original pigeons, there are exactly 8 pigeons in the brother's pigeon cage, how many pigeons and pigeon cages are there?

A: 27 pigeons and 4 cages?

Yes A and B have two shepherd boys, and A says to B, Give me one of your sheep, and my sheep will be twice as many as your sheep. B replied, "It is better to give me one of your sheep, so that we may have the same number of sheep, and each of the two shepherd boys shall have as many sheep."

A is x, B is y

x+1=2（y-1）

x-1=y+1

y=5x=7

Answer: A has 7 sheep and B has 5 sheep.

First of all, the price of Auchan rice is reduced by 10%**, in order to keep the total sales amount unchanged, how many percent of the sales volume should be increased compared with the original price of sales?

Let there be x people at the beginning x*1 80*2+(x+5)*1 80*8=3 4 solutions with x pigeon cages 6*x+3=8*x-5 solutions with x (x+1) 2+1=x-2 solutions to increase x solutions.