Xiao Ming bought several pencils at the price of 1 yuan and 3 pencils, and sold them all at the price of 2 yuan and 5 pencils. If he made 10 yuan, do you know how many pencils he sold?

Set X
（2/5-1/3）X=10
X=150

Xiao Ming went to the stationery store to buy the same quantity of ballpoint pens and pencils. The original price of ballpoint pens was 2 yuan and 3 yuan and 5 pencils. Because of the preferential promotion in the stationery store, both kinds of pens were sold
How many pens did Xiao Ming buy?

Suppose Xiao Ming bought a total of X ballpoint pens and X pencils, then he bought a total of 2x pens
Then: (2 / 3-1 / 2) x + (3 / 5-1 / 2) x = 8
(10/15+9/15-1)x=8
4/15 x=8
x=30
So Xiao Ming bought a total of 2x = 60 pens

Xiao Ming bought 4 exercise books and 3 pencils at the stationery store for 6.5 yuan. If the unit price of pencils is 1.5 yuan, what is the unit price of exercise books?

6.5-1.5*3=2
2÷4=0.5

How to deduce the vertex coordinate formula of quadratic function? Thank you for your detailed reasoning process

y=ax^2+bx+c
y=a(x^2+bx/a+c/a)
y=a(x^2+bx/a+b^2/4a^2+c/a-b^2/4a^2)
y=a(x+b/2a)^2+c-b^2/4a
y=a(x+b/2a)^2+(4ac-b^2)/4a
Axis of symmetry x = - B / 2A
Vertex coordinates (- B / 2a, (4ac-b ^ 2) / 4A)

Given the polynomial 4x2 + 1, add a term to make it a complete square. What methods do you have?

4X, - 4x, 4x4 let one of the terms sought be y, then (1) when y is the middle term, ∵ 4x2 + 1 ± y is the complete square form, ∵ 4x2 + y + 1 = (2x + 1) 2, ∵ 4x2 ± y + 1 = 4x2 + 4x + 1, ∵ y = ± 4x; and (2) when y is the tail term, 1 = 2 × 2x · y, then y = 116x2

If the length of a rectangle is reduced by 3cm, its area will be reduced by 15cm; if the width is reduced by 4cm, its area will be reduced by 36cm,
What is the area of the original rectangle in square centimeter?

If the length is reduced by 3cm and the area is reduced by 15cm, then the width is 5cm
If the width is reduced by 4cm and the area is reduced by 36cm, then the length is 9cm
So, isn't the area of a rectangle 5 × 9 = 45cm2

If K is negative, which quadrant does it pass through?
Such as the title

In y = K / x, if k > O, the image passes through one or three quadrants, and Y decreases with the increase of X
If K

Let f (x), G (x), be continuous on [a, b], be differentiable on (a, b), and the derivatives of F (x) g (x) are equal. This paper proves whether there is a constant C such that f (x) = g (x) + C

You should know that your problem is a corollary of Lagrange mean value theorem. First of all, we need to get a corollary from Lagrange mean value theorem: if the function f is differentiable on interval I, and the derivative of F = 0, then f is a constant function on I. let's prove your problem: as an auxiliary function f = F-G, because on (a, b), f (x) and G (...)

A. If the average score of a, B, C is 95; the average score of B, C, D is 94; a is the first place; E is the third place, 96 points; D is the best______ Points

A. The total score of B, C, is 95 × 3 = 285 (points), the total score of B, C, D is 94 × 3 = 282 (points), a is more than D: 285-282 = 3 (points), because e is the third place to test 96 points, so D has two possibilities: one is that D is less than e, since a is the first place and three points more than D, a can only score 98 points, while D is 95 points, and one of B and C scores 97 points, so, the other of B and C is the best A test score is: 285-98-97 = 90, which is contradictory to everyone's score greater than 91. Therefore, the ranking of D must be in front of E; that is, D is the second place; D is the second place, and the score is more than 96. Combined with a's 3 points more than D, we can see that D's score is 97, and a's score is 100. So the answer is: 97

Left and right translation law of inverse proportion function of first order function

All functions are in accordance with the law of left plus right minus
For example, y = x shifts 1 unit to the left to get y = x + 1
If y = x is shifted one unit to the right, y = X-1 is obtained
(feel it for yourself)

Xiao Ming bought several pencils at the price of 1 yuan and 3 pencils, and sold them all at the price of 2 yuan and 5 pencils. If he made 10 yuan, do you know how many pencils he sold?