There are two math problems that can t be solved!

2. The distance is 45 (21-1)=45 20=900m, and the new pile is 900 60+1=15+1=16.

Multiples of immovable stakes: first, 180m, 360m, 540m, last. The three immovable ones in the middle: 180m, 360m, and 540m.

In the middle, there are still moves: (21-2)-3=19-3=16.

If you think about it from the other side, the original 21 roots, minus the 5 roots that do not move (i.e., the common multiple) are 16 roots.

If a number is enlarged tenfold and is larger than the original, what is the original number?

Solution: Let this number be x, then there is an equation: 10x-x=, that is, 9x=, so x= every 45m according to a stake, plus a total of 21 stakes at both ends, now changed to every 60m by a stake, in addition to the starting stake does not move, how many stakes should be moved in the middle?

Solution: road length s=45 (21-1)=900m; The least common multiple of 45 and 60 is 180; 900÷180=5；Therefore it is not counted as the starting one.

Only 5 of the 20 stakes can be retained, so 20-5=15 need to be moved in the middle.

1。Solution: Let the original number be x

10x-x= from the title

9x=x=A: The original number is.

2。Solution: From the question, the least common multiple of 45 (21-1) = 900 (m) 45 and 60 is 180,900 180 = 5 (pieces) Answer: 5 wooden stakes need to be moved in the middle.

Wish. Thank you.

Solution: (1) Let y=k(x-3), and pass a(0, 4), so 4=-3k, k=-4 3

So y=-4 3 x+4

2) When t=2 seconds, op=2, and ob=3, so pb=13, so the circumference of obp=5+13.

3) When op=3, op=ob, obp is an isosceles triangle. When op=3, t=3 (sec).

E and f are the midpoints of ab and ac, respectively, and EF BC can be obtained, and EF = ?bc=AD, and AD ef

The intersection of EF and AD is the midpoint of AD (proportionality theorem).

Conclusion: The circle with EF as the diameter is tangent to the BC line segment (the distance between the two lines is half of the EF, i.e. the radius).

The planned selling price of product A is x yuan, then the planned selling price of commodity B is (1500-x) yuan (1+20%) x + (1-30%) (1500-x) = 1600x = 1100

1100x(1+20%)=1320 yuan.

Solution: If the original price of A is X yuan, then the original price of B is 1500-X

x(1+20%)+1500-x)(1-30%)=1600x=1100

Solution: Let A be set to x yuan, then B is (1500-x) yuan (1 20%) x (1500-x) (1-30%) = 1600120% x 1050-70% = 1600x = 1100 because 1500-x = 1500-1100 = 400, so A is 1100 yuan, and B is 400 yuan.

Solution: The original plan is to set a x yuan and B (1500-x) yuan.

x+20%x)+［1500-x〕-30%〔1500-x〕］=1600

1100 + (1 + 40%) = 1320 (yuan).

ae=4,ef=

Angular AEF = 90 degrees (Pythagorean inverse theorem).

Angle aeb angle fec = 90°

again b=90°

bae+∠aeb=90°

Loss of angular BAE = angular fec

Angle b = angle c

abe∽△efc

ab ce=be cf=ae ef=4 3, so let ab=4a then ce=3a

Write off the Qiao Pei strand be=4 root number (1-a 2).

Because of the square.

So be+ec=ab

The square of the two sides of the number 4a = 4 (1-a 2) + 3a and the solution is a 2 = 16 17

Square area = (4a) 2 = 16a = 16 16 17 = 256 17 because the angle apd = 60 degrees.

Angular bpa Angular DPC = 120°

b=60°

bap+∠bpa=120°

Angular bap = angular dpc

Angle b = angle c

abp∽△dpc

cp ab=dp ap=cd bp=2 3 let ab=a then cp=a 2 3

Because ab=bp+cp

So a=1+a2 3

So a=3 means that the side length of the triangle abc is 3

What percentage is the ratio of a black pentagram to a white pentagram? (The numerator retains two decimal places) 25 black pentagrams.

30 white pentagrams.

The ratio of a black pentagram to a white pentagram is: 25 30=

What percentage of the total number of black stars is a total of a star?

Step 1: Number of black stars + number of white stars = total number of stars.

Step 2: Number of Black Stars Multiply the total number of stars by 100

1.Solution: (Slow Game 1) 400 (100-80) = 20 points.

A: If two people start in the same direction at the same time, they will meet every 20 minutes.

2) 400 (100+80)=10 3 points.

Answer: If two people start in opposite directions at the same time and in the same place, they will meet every 10 3 minutes.

2.Untie; 50 km/h = 125 m/s

120+880) Bistool (125 9) = 72 seconds Answer: It takes 72 seconds for the train to leave the bridge completely from the start of the bridge.