At the stationery counter of a store, if 16 pencils are sold, the ratio of the number of pencils left to the number of pens is 1:3. If 52 pens are sold again, C At the stationery counter of a store, if 16 pencils are sold, the ratio of the number of pencils left to the number of pens is 1:3. If 52 pencils are sold, the ratio of the number of pencils left to the number of pencils is 2:5. How many pencils are there?

At the stationery counter of a store, if 16 pencils are sold, the ratio of the number of pencils left to the number of pens is 1:3. If 52 pens are sold again, C At the stationery counter of a store, if 16 pencils are sold, the ratio of the number of pencils left to the number of pens is 1:3. If 52 pencils are sold, the ratio of the number of pencils left to the number of pencils is 2:5. How many pencils are there?

Let the original pencil X and pen y be (x-16): y = 1:3, (y-52): (x-16) = 2:5. The solution is x = 36

Xiaohua bought a pen and B pencil cases in the store. It costs C yuan in total, D yuan for each pen. (1) express the price of each pencil case with a formula containing letters. (2) if a = 4, B = 6, C = 40.8, d = 2.4, please find out the price of each pencil case

(1) The unit price of stationery box is: (c-ad) △ B. (2) substitute a = 4, B = 6, C = 40.8, d = 2.4 into (c-ad) △ B. (c-ad) △ B. = (40.8-4 × 2.4) △ 6, = (40.8-9.6) △ 6, = 31.2 △ 6, = 5.2 (yuan). Answer: the price of each stationery box is 5.2 yuan

Can instantaneous velocity be obtained by derivative method
If we know the V-T diagram of a certain motion, can we get the instantaneous velocity at a certain moment through the derivative function

The number represented by the ordinate of V-T graph is the instantaneous velocity, so the derivative function is not needed to get the instantaneous acceleration at a certain moment!

How to calculate the weight per meter of pattern steel plate?
The calculation formulas of diamond, lentil and round beans are needed, not the theoretical weight table

Pattern coefficient X length x width

The perimeter of a rectangle is 24dm, and the decimeters of its length and width are prime numbers. What is the area of the rectangle
The perimeter of a rectangle is 24dm, and the decimeters of its length and width are prime numbers. How many square decimeters is the area of the rectangle?

Length + width = 24dm / 2 = 12dm
Because: the decimeters of its length and width are prime numbers, 12 = 5 + 7 (only in this case)
So: area of rectangle = 5 * 7 = 35 (square decimeter)

In the plane rectangular coordinate system, the parabola y = x ^ 2 + 2x + 3 is rotated 180 degrees around the point (- 1,0)?

From the meaning of the title, we know that the axis of symmetry of the parabola is x = - 1, draw the image, the opening upward, and the lowest point is (- 1,2),
Rotate 180 degrees around the point (- 1,0) to get (- 1, - 2). According to the symmetry, the intersection of the quadratic function and the X axis before rotation is (0,3). After rotation, the intersection is (0, - 3), so the analytical expression is y = - x ^ 2-2x-3

What are the materials for one cubic meter of ordinary concrete?

C15 cement 330 sand 619 gravel (2-4cm) 1315 water 160 (27.5 cement)
C20 cement 330 sand 618 gravel (2-4cm) 1315 water 167 (32.5 cement)
C25 cement 390 sand 561 gravel (2-4cm) River Stone 1309 water 170 (32.5 cement)
C30 cement 430 sand 530 gravel (2-4cm) 1309 water 170 (32.5 cement)
The foundation of your sentry box is C20 at most. (the gravel particle size can be 1-3cm according to the thinnest size of the component)

If the polynomial (4 * x * x + 1) is added with a monomial, it can become the complete square of a binomial integer, then the condition is satisfied

Add a 4x, 4x ^ 2 + 4x + 1 = (2x + 1) ^ 2

Is the curve integral of arc length in higher mathematics the approximate value of arc length?

1. The first kind of integration of arc length is to calculate the exact value of space curve, not approximate value, but exact value
2. The second kind of integral of arc length does not calculate the arc length of space curve
If it's a math teacher, it's a boring pure math game
If it is physics, astronomy, hydrology, electronics, electrical and other teachers, generally have very obvious physical significance
The general physical meaning refers to the work, circulation, mass, electricity and so on

Conversion table of area units

1 square kilometer = 100 hectare 1 hectare = 10000 square meter 1 square meter = 100 square decimeter 1 square decimeter = 100 square centimeter 1 square centimeter = 100 square millimeter