The problem of putting books on the upper and lower shelves, The number of books on the upper and lower layers of the bookshelf is the same. 25% of the books on the upper layer are borrowed, and 2 / 5 of the books on the lower layer are borrowed. Then 15 books are taken from the upper layer to the lower layer. At this time, the number of books on the upper and lower layers is the same. How many books are there on the upper and lower layers of the bookshelf? It's urgent to have a formula and an answer

Little wonderful princess,
Take 15 books from the upper level to the lower level. If the number of books on the upper and lower levels is the same, the upper level has more books than the lower level
15 × 2 = 30
The upper layer is left with:
1－25%＝75%
The lower layer is left with:
1－2/5＝3/5
The original two floors are:
30 (75% - 2 / 3) = 360 (this)
Take 15 books from the upper layer to the lower layer. At this time, the number of books on the upper and lower layers is the same
360 △ 2 = 180

All the 3350 newly purchased books should be put into the bookshelf. Each bookshelf can hold 270 books at most, and at least () bookshelves are needed

13 bookshelves

There are 24 identical bookshelves in a library. Each bookshelf has 4 layers and each layer holds 240 books. How many books can these bookshelves hold?

240 × 4 × 24, = 960 × 24, = 23040 (copies). Answer: these bookshelves can hold 23040 copies per person

Famous aphorisms and poems about the Yellow River

There are many contents, and some of them are repeated. You can choose according to your needs. The desert is straight, and the long river is falling with the Japanese yen

What is the result of (3mn-5m to the power of 2) - (3m to the power of 2-5mn)

From the theme, (3MN - (5m) ^ 2) - ((3m) ^ 2-5mn) = 3mn-25m ^ 2-9m ^ 2 + 5MN = 8mn-34m ^ 2 = 2m (4n-17m)

The solution set of quadratic inequality ax ^ 2 + BX + C > 0 is r if and only if a why > 0, B ^ 2-4ac why

If the solution set of quadratic inequality ax ^ 2 + BX + C > 0 is r
Then the parabola y = ax ^ 2 + BX + C must be all above the x-axis
So the opening of parabola y = ax ^ 2 + BX + C must be upward and a > 0
If the parabola y = ax ^ 2 + BX + C has no common point with the X axis, the discriminant = B ^ 2-4ac is required

How to say in English in the library?

In (at) the library

The number of integer solutions of inequality x with absolute value ≤ 3 is
The number of integer solutions of inequality x with absolute value ≤ 3 is ()
A3, B4, C6, D7

-3 ≤ x ≤ 3, so there are - 3 - 2 - 10 1 2 3 7 selected D

Given that the function f (x) is a decreasing function on the interval (0, + ∞), then the relation between F (a2-a + 1) and f (34) is______ ．

∵ a 2-A + 1 = (A-12) 2 + 34 ≥ 34, and the function f (x) is a decreasing function on the interval (0, + ∞), so the answer is: F (a 2-A + 1) ≤ f (34)

Merge congeners - 5 / 3 (x + y) &# 178; - 6 (x + y) + 3 (x + y) &# 178; + 4 / 3 (x + y)

-5/3（x+y）²-6（x+y)+3(x+y)²+4/3（x+y）
=4/3（x+y）²-14/3（x+y)