It took 25 seconds for a train to pass through a 386 meter railway bridge, followed by 17 seconds for it to pass through a 236 meter long tunnel. How many meters does this train travel per second?

（386-236）÷（25-17）
=150÷8
=18.75 M / S

After cutting a circular piece of paper, put it together into an approximate rectangle with the width equal to the radius and the area unchanged. The perimeter of the rectangle is 16.56 cm. What is the area of the cut circular piece of paper in square cm?

Let the radius of this circle be r. according to the meaning of the question, we can get: 2 × 3.14r + 2R = 16.56, & nbsp; & nbsp; 6.28r + 2R = 16.56, & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; 8.28r = 16.56, & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; r = 2, 3.14 × 22, = 3.14 × 4, = 12.56 (square centimeter). Answer: the area of the paper is 12.56 square centimeter

Given that the general term formula of the sequence {an} is an = log2 [(3 + n ^ 2) - 2], then which term is log2 (3)?
[(3 + n ^ 2) - 2] is an index, and (3) is an index
Please write the detailed process

Do you have a wrong number? [(3 + n ^ 2) - 2], followed by subtraction, it turns out that n is the root sign 2

The taxi charging rule is that 7 yuan will be charged for driving within 3 km, and 1 yuan will be charged for every kilometer after driving more than 3 km (less than 1 km, calculated as 1 km)
1) How much should I pay if I take 11.24 km?
2) If a passenger paid 11 yuan, how far did he travel

1. Charge = 7 + (11.24-3) * 1 = 15.24 yuan
2. (11-7) △ 1 + 3 = 7 km
If you have something you don't understand, please ask again. I wish you progress in your study and make progress! (*^__ ^*)

In the pyramid p-abcd, the bottom surface ABCD is a rectangle, and PA ⊥ plane ABCD, PA = 5, ab = 4, ad = 3, find the angle between the line PC and the plane ABCD

Link AC
In rectangular ABCD, BC = ad = 3, ab = 4, ∠ ABC = RT ∠
AC=5
Because: PA ⊥ plane ABCD
So: PA ⊥ AC, the angle between the straight line PC and the plane ABCD is ∠ PCA
And PA = 5 = AC
Therefore, PCA = 45 degree
So the angle between PC and ABCD is 45 degrees

What is the quality of writing a pencil?

Pencil has many uses, people also have a lot of future, don't abandon yourself

Math 101
Two tractors deliver fertilizer to the farm. The first one drives from the warehouse to the farm at a speed of 9 kilometers per hour. 30 minutes later, the second one drives from the warehouse to the farm at a speed of 12 kilometers per hour. How far is the second one from the warehouse to catch up with the first one?

30 minutes later, the first vehicle is 9 * 0.5 = 4.5km away from the warehouse
At this time, it will take 4.5 / (12-9) = 1.5 hours for the second car to catch up with the first one
So the first car took 1.5 + 0.5 = 2 hours to catch up
So catch up according to the warehouse distance
2 * 9 = 18 km

As shown in the figure, in the quadrilateral ABCD, ad = BC, ∠ DAB = 50 ° and ∠ CBA = 70 °, P, m and N are the midpoint of AB, AC and BD respectively. If BC = 8, then the perimeter of △ PMN is______ ．

∵ P and N are the middle points of AB and BD, PN = 12ad = 12 × 8 = 4, PN ∥ ad, ∥ NPB = ∥ DAB = 50 °, similarly, PM = 4, ∥ MPa = ∥ CBA = 70 °, ∥ PM = PN = 4, ∥ MPN = 120 ° - 50 ° - 70 ° = 60 °, ∥ PMN is an equilateral triangle, ∥ Mn = PM = PN = 4, ∥ PMN's perimeter is 12

A car drives from the east to the West. After a journey, it is 210 kilometers away from the west, and then 20% of the whole journey. At this time, the ratio of the distance traveled to the distance not traveled is 3:2. How many kilometers are there between the East and the west?

Let x-210 + 20% x = 35x, x-210 + 0.2x = 0.6x, & nbsp; 1.2x-210 = 0.6x, & nbsp; 1.2x-0.6x = 210, & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; 0.6x = 210, & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; X = 350. A: the East and West cities are 350 km apart

Simple calculation: 1 / 2 + 1 / 6 + 1 / 12 + 1 / 20 + 1 / 30 + 1 / 42 + 1 / 56 + 1 / 72 + 1 / 90

=1/2+1/2*3+1/3*4+1/4*5+1/5*6+1/6*7+1/7*8+1/8*9+1/9*10
=1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10
=1-1/10
=9/10

It took 25 seconds for a train to pass through a 386 meter railway bridge, followed by 17 seconds for it to pass through a 236 meter long tunnel. How many meters does this train travel per second?