-3. How much is the sum of + 5, - 7 less than the sum of their absolute values?

-3. How much is the sum of + 5, - 7 less than the sum of their absolute values?

(| - 3 | + | - 5 | + | - 7 |) - (- 3 + 5-7) = 15 - (- 5) = 20

There is an equal width sidewalk around a 70 m long and 50 m wide rectangular green space. The area of this sidewalk is 1300 square meters. The width of this sidewalk is calculated

Let the width of sidewalk be a
Then 2 * (70 + 2 * a) * a + 2 * 50 * a = 1300
a²+60a-325=0
(a+65)*(a-5)=0
The solution is a = - 65 or a = 5
Since the width can not be negative, the width of sidewalk can be 5m

A and B start from point a at the same time on the circular track and run in the opposite direction. A's speed is 7 meters per second, and B's speed is 8 meters per second. How many times have a and B met for the first time (not at point a) until they first met again at point a?

If you run in the opposite direction, if you meet at point a, the number of laps you run at the same time is an integer. The ratio of a's speed to B's speed is 7:8, so when a runs 7 whole laps, B just runs 8 whole laps. At this time, two people meet at point a
Because running at the same time on the track will meet twice in every whole lap, B ran 8 laps, and then subtracted the first lap when they started at a, so 8 * 2-1 = 15
The two met 15 times from the first time to the second time

All the ancient poems from grade one to grade six of Jiangsu Education Press

（1） There are four or five places in Yancun, six or seven pavilions and eighty or ninety flowers in Jiangnan. There are lotus leaves in Jiangnan. Fish play among lotus leaves: fish play in the east of lotus leaves, fish play in the west of lotus leaves, fish play in the south of lotus leaves, fish play in the north of lotus leaves

Under the microscope, the shape of a cell in the human body can be approximately seen as a circle. Its diameter is 1.6X10 minus 6 cubic meters. Using a scientific calculator to calculate the area of this cell (π = 3) is fast!
It's a process. Thank you~

πd²/4=3*0,64*10^（-12）=1.92*10^（-12）
In fact, it should be the sphere area, and the cell is three-dimensional, so the sphere surface area is π D & # 178;, which is four times of the above area

The construction area is 90 square meters, and the sharing rate is 20%!

Building area = inside area + sharing
112.5=90+22.5
Shared coefficient = shared area / built-up area
0.25=22.5/90

Xiao Wang's walking speed is 4.8 km / h, and Xiao Zhang's walking speed is 5.4 km / h. they go from place a to place B. Xiao Li's cycling speed is 10.8 km / h, from place B to place a. the three of them set out at the same time. Five minutes after Xiao Zhang and Xiao Li met, Xiao Wang and Xiao Li met again. Q: how long does it take Xiao Li to ride from place B to place a______ Points?

5 minutes = 112 hours, (4.8 + 10.8) × 112, = 785 × 112, = 1310 (km), 1310 ^ (5.4-4.8), = 1310 × 53, = 136 (hours), (5.4 + 10.8) × 136 ^ 10.8, = 815 × 136 × 554, = 134 (hours), = 195 (minutes); answer: it takes 195 minutes for Xiao Li to ride from place B to place a

English proper form 2
many people surf the internet ___ for information every day
Many people surf the Internet___ （look） for information every day

to look /in order to

What are the scientific causes of solar and lunar eclipses

Solar eclipse is because the moon is between the sun and the earth
An eclipse is because the earth is between the moon and the sun
When the earth revolves around the sun and the moon revolves around the earth, there are always three points in a straight line

The answers to the final classification review and examination of the fifth grade mathematics volume I
Section 12.14.15.17.29.30.31.32.36.37.38.39.40
In a cage, there are chickens and rabbits. Count their heads and feet. There are 20. How many chickens and rabbits are there
To solve the equation

One variable linear equation: let x chickens. 2x + 4 (7-x) = 202x + 28-4x = 2028-2x = 202x = 8x = 47-x = 3 answer: there are 4 chickens and 3 rabbits. Also, let x rabbits. Two variable linear equation: let x chickens and Y rabbits. X + y = 7 2x + 2Y = 14 2x = 4Y = 20 2x + 4Y = 20 2x = 6y = 3x = 4 answer: there are 4 chickens and rabbits