There is a railway bridge with a length of 1000 meters. A train passes through the bridge. It takes 120 seconds for the train to get on the bridge and get off the bridge completely. The time for the whole train to be completely on the bridge is 80 seconds. What are the speed and length of the train?

Let the speed of the train be x m / s and the length of the train body be y m, and the relationship between them is listed. The equations are 120x = 1000 + y, ①, 80x = 1000-y, ②, which are solved by ① and ②: x = 10 m, y = 200 m. a: the speed and length of the train are 10 m / s and 200 m respectively

If the circumference of a rectangle is 40 cm and the width is x cm, the equation is ()

Length = 40 △ 2-x

Given m power of 16 = a, n power of 4 = B, find 5m + 2n power of 2

It is known that m power of 16 = a, 2 ^ (4m) = n power of a 4 = B 2 ^ (2n) = 5m + 2n power of B 2 = [2 ^ (4m)] ^ (5 / 4) * 2 ^ (2n) = a ^ (5 / 4) * B

If it takes more than 3 minutes to make a phone call to a certain place, it will cost 0.5 yuan. If it takes more than 3 minutes and less than 1 minute, it will cost 0.3 yuan. Xiao Li will pay 2 yuan for a phone call to a certain place
How many minutes did he play?

(2-0.5) / 0.3 = 5 minutes,
5 + 3 = 8 minutes

As shown in the figure, in rectangular paper ABCD, ad = 9, ab = 3, fold it so that point d coincides with point B, and the crease from point C to point C 'is EF?

Let BF = x, then AE = ad-de = 9-x. in RT △ Abe, ∠ BAE = 90 °｜ be2 = AB2 + AE2, that is, X2 = 32 + (9-x) 2, the solution is x = 5, ｜ BF = 5, ｜ s △ bef = 12bf · H = 12 × 5 × 3 = 152

Xiaoya bought 10 pencils of 0.4 yuan and 0.6 yuan each, paid 5 yuan to get 0.4 yuan back, and bought several pencils for each

Suppose: X pens of 0.4 yuan and Y pens of 0.6 yuan from xiaoyamai
0.4X+0.6Y=5-0.4；
X+Y=10；
The solution of the equation is x = 7, y = 3
So Xiaoya bought 7 pens of 0.4 yuan and 3 pens of 0.6 yuan

Taxi starts at 7 yuan per kilometer, and then charges 1.10 yuan per kilometer (less than 1 kilometer is calculated as 1 kilometer). If Xiao Ming takes a taxi from home to school, how much is the taxi fee? Xiao Ming takes a taxi from home to school for 3.5 kilometers

7 + 1.1 = 8.1 (yuan)

A cuboid with a height of 40 cm and a square bottom will increase its surface area by 80 cm if its height is increased by 5 cm. How about the surface area and volume of the original cuboid?

Increased surface area = increased height of base perimeter x
Perimeter of bottom surface = 80 △ 5 = 16cm
So the side length of the bottom surface is 16 △ 4 = 4cm
Surface area = 2 square bottom area + side area = 2 x 4 & # 178; + 16 × 40 = 672cm & # 178;
Volume = 4 * 4 * 4 = 64

It was originally planned to take 5 hours and 30 minutes for Li Ping to ride a bicycle from his home to the county. Due to the uneven road of 3.6 kilometers on the way, the speed is equivalent to 0.75 of the original speed, so he arrived 12 minutes late. How many kilometers is the distance between Li Ping's home and the county?
I know the correct answer. I just want to ask what's wrong with my answer?
My solution: 3.6 (12 / 60) = 18 (slow speed in 3.6 km)
18 △ 0.25 = 72 (because the speed in 3.6 km is the original 0.72, which is 0.25 slower than the original), so 72 is the amount of unit one, which is the original speed
Then I'll add 72 × 5.5 = 396 (km)
What's wrong with what I think?
When I asked a question, I didn't express it very clearly. The first step I worked out was [3.6 ^ (12 ^ 60) = 18, which means that the speed difference between the original speed and the slow speed is 18. Since the speed difference is exactly the original 0.25, I'm 18 ^ 0.25. Is this 18 not the speed difference? That's what I haven't figured out.

The time ratio of 3.6km uneven road to 3.6km level road is 1:0.75 = 4:3
That is, the average road time, (12 / 60) / (4-3) / 3 = 0.6 hours
Level road speed: 3.6 △ 0.6 = 6 km / h
Distance from home to the county: 6 * 5.5 = 33 km
The first step is wrong
Because of the same 3.6 km, the time ratio of level road to uneven road is 3:4
12 minutes is only 1 / 3 of the time on a level road, which is equivalent to the time required for 3.6 kilometers on a level road, which is (12 / 60) / (4-3) / 3 = 0.6 hours
So 3.6 △ 12 △ 60 = 18 is wrong

The most commonly used mathematical problems in daily life

Hongshi village primary school is divided into six groups to water trees. There are four people in each group. A total of 360 trees are watered. How many trees are watered per person? The number of a box of eggs is three times that of a basket of eggs. There are 96 eggs in a box, and how many eggs are there in six baskets? Uncle Wang's orchard harvests 358 kg of apples, 270 kg of pears, 196 kg of plums