Xinhua Bookstore sold 680 new books on the first day, 50 less than the second day. The number of new books sold on the third day was 1.2 of the second day. How many new books were sold on the third day?

Xinhua Bookstore sold 680 new books on the first day, 50 less than the second day. The number of new books sold on the third day was 1.2 of the second day. How many new books were sold on the third day?

﹙680+50）×1.2=876
876 new books sold on the third day

Xinhua Bookstore bought a batch of new books. In the first week, it sold 1 / 2 of the total number. In the second week, it sold 250 books. In the third week, it sold half of the first two weeks, with 350 books left. How many new books did Xinhua bookstore buy

1100

Add another number to make it proportional to 0.16, 0.32, 2 / 5, and write it out?
The key is that there are () answers to this number? Why?

Let these four numbers be a (0.16), B (0.32), C (2 / 5) and D respectively. D is the required number
To form a proportion, there are no more than the following three situations
ab=cd …… ① (i.e. a / C = D / B or a / D = C / B, but their corresponding D values are the same, so they are considered as a type, the same below)
ac=bd …… ②
ad=bc …… ③
d①=0.128
d②=0.2
d③=0.8

Let a and B be matrices of order n, and ab = ba. It is proved that if a and B are similar to diagonal matrices, then there is an invertible matrix P such that P ^ - 1AP and P ^ - 1bp are diagonal matrices

S ^ - 1As = C = diag (A1 * I1, A2 * I2,..., AR * IR) is divided into R blocks, each block has the same eigenvalue, II is the unit matrix, SCS ^ - 1B = AB = Ba = BSCs ^ - 1, multiply s ^ - 1 left, multiply s right, get CS ^ - 1BS = s ^ - 1bsc, note g = s ^ - 1BS, then CG = GC, because C is a diagonal matrix, and G and C are commutative, it is easy to know that g = diag (G1, G2,..., GR)

Find all four digits that satisfy the following conditions: can be divided by 111, and the quotient is equal to the sum of the four digits

If a × 103 + B × 102 + B × 102 + C × 10 + D can be divided by 111, then a × 103 + B × 102 + C × 10 + D = 9A + B + B + B × 102 + C × 10 + D111 = 9A + B + B + B × 102 + C × 10 + D111 = 9A + B + B + B × 102 + C × 10 + D = 9A + B × 102 + C × 10 + D111 = 9A + B + B × 102 + C × 10 + d1111 = 9A + B + B + B + B + B × 102 + C × 10 + D111 = 9A + B + B + B + B + C + D, that is, 8a, 11b = 9 (a + C) ③, from C + D = 8a, and the maximum value of C + D + D + D + D + D + D + D + D is 9 + 9 + 9 + 9 = 9 + 9 = 18, know a = 1 or a = 2, know a = 1 or a = 2, know a 2, C = 9 , d = 7, so the four digit is 2997

The product of two matrices is zero. What is the relationship between their ranks

Let AB = 0, a be mxn, B be NXS matrix
Then the column vectors of B are all solutions of AX = 0
So r (b)

Equation 3.5x + 2 (x-4.5) = 7.5 the quotient of a divided by B is 4, the remainder is 3, a is 39 more than B, how much is a?

3.5x+2(x-4.5)=7.5
35x+20x-90=75
55x=165
x=3
Let a be a, then B be a-39
According to the meaning of the title
4×（a-39）+3=a
4a-156+3=a
3a=153
a=51
A is 51

(1) 8050 to 0______ Yes, there are______ A significant number, yes______ (2) the number is 4.8 × 105______ Yes, there are______ A significant number, yes______ (3) the number is 53100______ Yes, there are______ A significant number, yes______ ．

(1) The number 0.8050 is accurate to ten thousand digits, and there are four significant digits, namely 8, 0, 5, 0; (2) the number 4.8 × 105 is accurate to ten thousand digits, and there are two significant digits, namely 4, 8; (3) the number 53100 is accurate to hundred digits, and there are three significant digits, namely 5, 3, 1

Zhang Hua read a story book. On the first day, he read one third of the whole book. On the second day, he read 20 pages. At this time, he saw half of the whole book. How many pages are left?

Pages:
20÷（1/2-1/3）
=20÷1/6
=120 (page)
Remaining:
120 × 1 / 2 = 60 (page)
May I help you!

It is known that a and B are opposite to each other, m and N are reciprocal to each other, and the absolute value of X is 2. Find the value of formula X & # 178; + 2a-3mn + 2B

Let's know that a and B are opposite numbers, m and N are reciprocal numbers, the absolute value of X is 2, and find the value of formula X & # 178; + 2a-3mn + 2B
Satisfy a + B = 0 Mn = 1 x = ± 2
x²+2a-3mn+2b
= 4 + 2 (a+b) -3mn
= 4 + 0 - 3
= 1
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