The school has two kinds of books, science and technology books and literature and art books. Among them, science and technology books are 4 / 9 of literature and art books. Now we have bought another 560 science and technology books. At this time, literature and art books account for 45% of the total. How many books are there in total?

The school has two kinds of books, science and technology books and literature and art books. Among them, science and technology books are 4 / 9 of literature and art books. Now we have bought another 560 science and technology books. At this time, literature and art books account for 45% of the total. How many books are there in total?

Suppose there are x books of literature and art, then there were 4x / 9 books of science and technology, there were 4x / 9 + X books in total, now 560 books of science and technology have been bought, there are 4x / 9 + X + 560 books in total, X / (4x / 9 + x + 560) = 45%, and we get x = 720, now there are 1600 books in total

Six year math problems in primary school
To build a section of road, team a needs 20 days to complete the construction, while team B needs 25 days to complete the construction. At the beginning, the project headquarters arranged team a to repair this section of road, but after team a repaired it for a few days, due to other tasks, the headquarters arranged team B to continue to repair it. In this way, it takes 23 days to complete the construction of this section of road?
(do it in the way of grade 6 or below, with a detailed process, preferably in words, just like a short commentary.) thank you

Suppose the total workload is 1, because it takes 20 days for team a to complete the repair alone, so the work efficiency of team a is 1 / 20; Team B needs 25 days to complete the repair alone, so the work efficiency of team B is 1 / 25

The apples in basket a are 14 kg heavier than those in basket B. after basket a sells 47 and basket B sells 25, the remaining apples in the two baskets are equal in weight. How many kg of apples are there in basket a?

If a and B are non-zero real numbers, then the following inequalities are: ① A2 + B22 ≥ AB; ② (a + b) 24 ≤ A2 + B22; ③ a + B2 ≥ ABA + B; ④ Ba + ab ≥ 2
A. 4B. 3C. 2D. 1

a. If B is a non-zero real number, ① ∵ (a-b) 2 ≥ 0, then A2 + B22 ≥ AB can be obtained by expansion; ② ∵ (a-b) 2 ≥ 0, then A2 + B2 ≥ 2Ab, ∵ 2 (A2 + B2) ≥ (a + b) 2, ∵ (a + B) 24 ≤ A2 + B22; ③ if a = b = - 1, then a + B2 ≥ ABA + B does not hold; ④ if AB < 0, then Ba + ab ≥ 2 does not hold

Three quarters of B is equivalent to A. B is 40. What's one third of a? Two seventh of a number is 8. What's three quarters of a number?
Two out of seven of a number is 8. What's three out of four of this number?
Two fifths of the number a is equal to four fifths of the number B. what is the number B and 60 of the number a?

Three quarters of B is equivalent to A. B is 40. What's one third of a?
40×3/4×1/3
=30×1/3
=10
Two out of seven of a number is 8. What's three out of four of this number?
8÷2/7×3/4
=28×3/4
=21
Two fifths of the number a is equal to four fifths of the number B. what is the number B and 60 of the number a?
60×2/5÷4/5
=24÷4/5
=30

The solution set of inequality X-2 with x 1 greater than 0 is?

The inverse proportion function transforms fractions into product forms, which means finding out the same sign of numerator and denominator is the solution set
(x+1)/(x-2)>0
(x+1)(x-2)>0
x2

When a car goes from city a to city B, it travels 60 kilometers per hour, and when it comes back, it travels 40 kilometers per hour

If the average speed is x and the distance between the two places is y, then the time to go is Y / 60 and the time to come back is Y / 40. The average speed is x = 2Y / (Y / 60 + Y / 40). The average speed of solving the equation is 48, so the average speed is 48

The inequality x ^ 2-mx-2m ≤ 0 has real number solution, and for any real number solution x1, X2 has | x1-x2 | ≤ 3, find the value range of real number M
The correct answer is [- 9, - 8] ∪ [0,1],

X ^ 2-mx-2m ≤ 0 has real number solution, x ^ 2-mx-2m = 0 has real number solution
Then the discriminant = m ^ 2 + 8m ≥ 0 and the sum of the two is m, the product is - 2m
For any real number solution x1, X2, there must be | x1-x2 | ≤ 3
0≤(x1-x2)^2=(x1+x2)^2-4x1x2≤m^2+8m≤9
We obtain m ∈ [- 9, - 8] ∪ [0,1]

From place a to place B, it takes 12 hours for a bus and 15 hours for a freight car. The two cars want to set out from both places. When they meet, the bus travels 98 kilometers more than the freight car
It takes 12 hours for a bus and 15 hours for a freight car to go from a to B. the two cars start from a and B. when they meet, the bus runs 98 kilometers more than the freight car

The distance is fixed and the speed is inversely proportional to the time
So the speed ratio of bus to loan car is: 15:12 = 5:4
When the two cars meet, the bus goes more than the loan car: (5-4) / (5 + 4) = 1 / 9
The distance between a and B is: 98 ÷ (1 / 9) = 882km

As shown in the figure, the coordinates of point a are (- 3, - 4) and the coordinates of point B are (5,0)
(1) Explain why OA = ob
(2) Find the area of △ AOB
(3) Find the distance from the origin o to ab

0A=√(3²+4²)=5 OB=5 QA=OB
S△AOB=1/2*5*4=10
AB = √ (8 & # 178; + 4 & # 178;) = √ the distance from 80 o to AB is 1 / 2H * AB = 10 h = 10 * 2 / √ 80 = √ 5