There are 2400 popular science books and literature and art books in the library of a residential area, of which literature and art books are 1.5 times of popular science books. How many popular science books are there? It's just a formula, not a calculation

There are 2400 popular science books and literature and art books in the library of a residential area, of which literature and art books are 1.5 times of popular science books. How many popular science books are there? It's just a formula, not a calculation

2400x (1 / 1 + 1.5) = popular science books

The library of the school bought back three sets of interesting books and five sets of popular science books for a total of 919 yuan. It is known that each set of popular science books is 125 yuan. How much is each set of interesting books?

(919-5 times 125) divided by 3 = 98 (yuan)

Mr. Liu went to the bookstore to buy books. Because of the large quantity of books, the shopkeeper gave a 20% discount. Therefore, Mr. Liu could buy five more books with 120 yuan. What was the original price of this book?

120 × 20% / 5% / 80% = 24% / 5% / 80%, = 4.8% / 80%, = 6 yuan. A: the original price of this book is 6 yuan

Poems, sayings and idioms about horses

In a word, it's hard to catch a horse, to scare a mule before a gun, to take the lead, to watch a flower on a horse, to take office on a horse, to have a smooth horse, to have a heart ape on a horse, to have an old horse know his way, and to jump a horse

If the line y = ax + B (AB ≠ 0) is not the third quadrant, then the quadrant of the vertex of the parabola y = AX2 + BX is ()
A. One B. two C. three D. four

∵ if the line y = ax + B (AB ≠ 0) is in the third quadrant, then a ＜ 0, B ＞ 0, − B2A ＞ 0, 4ac − b24a ＞ 0, and the quadrant where the vertex of the parabola y = AX2 + BX is in is the first quadrant

The weight of a cubic stone

1600kg/m3

Factorization of polynomial a ^ 2 + 3AB + 2B ^ 2
In 3 minutes, hurry, hurry, good people will be rewarded!

（a＋b）×（a＋2b）

CoV (x, y) = e (XY) - E (x) e (y) in covariance. How to calculate e (XY) here, for example

Xi 1.11.9 3yi 5.0 10.4 14.6e (x) = (1.1 + 1.9 + 3) / 3 = 2e (y) = (5.0 + 10.4 + 14.6) / 3 = 10e (XY) = (1.1 × 5.0 + 1.9 × 10.4 + 3 × 14.6) / 3 = 23.02cov (x, y) = e (XY) - E (x) e (y) = 23.02-2 × 10 = 3.02 in addition: D (x) = e (X & # 178;) - E & # 178

What is the conversion table of force units?

1 Newton (n) = 0.225 LBF = 0.102 KGF
1 KGF = 9.81 n
LBF = 4.45n (n) dyn = 10-5n (n)

-1 + 2-3 + 4 -... - 97 + 98-99 + 100,

-1+2-3+4-...-97+98-99+100
=（-1+2）+（-3+4）+...（-99+100）
=1+1+...+1
=1*50
=50