Mr. Wang bought back some exercise books. If he was equally divided into four classes, he would get two more. If he was equally divided into five classes, he would get three more. The exercise books were between 80 and 100 all the time

Mr. Wang bought back some exercise books. If he was equally divided into four classes, he would get two more. If he was equally divided into five classes, he would get three more. The exercise books were between 80 and 100 all the time

That is to say, if you buy two more books, you can get an average of four classes or five classes
The common multiple of 4 and 5 minus 2 is between 80 and 100
100-2 = 98

Mathematical solution (you can write down the formula or the idea of the answer,
An empty cuboid container is 50 cm long, 40 cm wide and 30 cm high. The other one is also a cuboid. The container is 40 cm long and 30 cm wide, and it contains 24 cm deep water. Pour the water container into the empty cuboid until the water in the two containers is the same height. At this time, the water depth is several cm

Volume of water in container: 40 × 30 × 24 = 28800 cm3
Bottom area of empty container: 50 × 40 = 2000 square centimeter
Bottom area of water container: 40 × 30 = 1200 square centimeter
Height of water poured into two containers: 28800 △ 2000 + 1200 = 9cm

Several elementary equations to solve practical problems, urgent
1. It takes 4 hours for a ship to sail from place a to place B downstream, and 40 minutes more to sail upstream than downstream. It is known that the ship travels 16 km / h in still water to calculate the water velocity. If the water velocity is x km / h, then the following equation is correct_________ .
A.4*（16+x）=（4+2/3）*（16-x） B.4*16=（4+2/3）*(16-x)
C.4*（16+x）=（4+0.4）*（16-x） C.4*(16+x)=(4+2/3)*16
2. For a project, it takes 8 days for team a to do it alone, 9 days for team B to do it alone, 3 days for team a to do it, 3 days for team B to support, and 3 / 4 of the task for team B to do it in X days________ .
3. A workshop assembles 6 machine tools every day. It is estimated that a batch of machine tools will be assembled in a few days. After 1 / 3 of these machine tools are assembled, the process level is improved and the work efficiency is increased to 4 times of the original. The result is 10 days ahead of schedule. What is the number of these machine tools?
The first one is choice. The second one is only equation. The third one is equation, process and answer

1. Acceleration along the water, deceleration against the water (16 + x) * 4 = (16-x) * (4 + 2 / 3) so choose A2. A's speed is 1 / 8, B's speed is 1 / 9. A completes 3 / 8 in three days, B completes X / 9 in X / 9. The 3 / 4 column of two people completes the task is 3 / 43. Suppose that 4 * 6 * (X-10) = 6 * x * 2 / 324x-240 = 4x20x = 12 in x = 12

Simple formula of 0.4 × 77 + 0.8 × 99

0.4×77＋0.8×99＝0.4×7×11＋0.8×9×11＝2.8×11＋7.2×11＝﹙2.8＋7.2﹚×11＝10×11＝110

Find limx → 0 [radical a ^ 2 + x-a] / x, (a > 0) the radical covers a ^ 2 + X

You just multiply the fraction up and down by one (root a ^ 2 + X + a), and then you take x = 0 and get 1 / 2A

On the answers of P59 / exercise 1 in Volume 1 of junior high school
As the title!
1. Draw any △ ABC and make the following rotation:
(1) Take a as the center and rotate the triangle 40 ° counterclockwise;
(2) Turn the triangle clockwise by 60 degrees;
(3) Take any point outside the triangle as the center and rotate it clockwise by 120 degrees;
(4) Rotate the triangle 180 ° around the midpoint of AC.

It's not difficult to rotate the drawing
You need to find the center of rotation, find out the direction of rotation, and finally grasp the degree of rotation
Pay attention to the corresponding points when drawing. For example, in question 1, the new triangle is a'b'c '
So AB = ab ', angle bab' = 40 degrees
Finally, connect the corresponding a'b'c '

(15-5) times 5 / 13 + 8 / 13 times 20 times 5 percent equals

58/13

A sentence that describes the inner feelings of a character in a story

Jiangsu Education Edition Grade 7 Volume 1 mathematics problems
If a and B are two rational numbers, a new operation "*" is defined, that is, a ⁃ B = 2Ab, then the value of 5 ⁃ 3 is ()
A -15 B -20 C -30 D 30

D

2X + (93-x) = 138 solution equation

2x+(93-x)=138
2x+93-x=138
2x-x=138-93
x=45