When a batch of machine parts are processed, the master can do it alone for 5 hours, and the apprentice can do it alone for 2 hours to complete 1 / 4 of this batch of parts How many parts are there in this batch?

When a batch of machine parts are processed, the master can do it alone for 5 hours, and the apprentice can do it alone for 2 hours to complete 1 / 4 of this batch of parts How many parts are there in this batch?

The apprentice worked alone for 2 hours to complete 1 / 4 of this batch of parts, and the apprentice worked for 8 hours
Set up the master to divide into x every hour
5x = 8 (X-6), x = 16
That is, there are 80 parts

Solve the equation 1.2x + 3.8x = 5.5
In three minutes, or it's invalid

12x+38x=5.5
　　5x=5.5
　　x=1.1

Warehouse A has 100 tons of grain and warehouse B has 80 tons of grain. Warehouse A has transported a batch of grain to warehouse B. at this time, the grain in warehouse A is exactly 45 tons of that in warehouse B. how many tons of grain has warehouse a transported to warehouse B?

(100 + 80) × 44 + 5, = 180 × 49, = 80 (tons), 100-80 = 20 (tons), a: warehouse a transported 20 tons of grain to warehouse B

X-3 / 7X = 1 / 2 solving equation with process

4/7X=1/2 x=7/8

0.75 + (- 11 / 4) + 0.125 + (- 5 / 7) + (4 and 1 / 8) + 0.25

Math problem:
0.75 + (- 11 / 4) + 0.125 + (- 5 / 7) + (4 and 1 / 8) + 0.25
=(0.75 + 0.25) + (0.125 + 4 1 / 8) - 11 / 4-5 / 7
=1 + 4 and 1 / 4-2 and 3 / 4-5 / 7
=5 and 1 / 4-2 and 3 / 4-5 / 7
=2 and 1 / 2-5 / 7
=1 and 11 / 14

If the first n terms in the equal ratio sequence {an} and Sn = 3 ^ n + R, then R is equal to ()
A.-1 B.0 C.1 D.3

What a difficult way!
From the title, we know that A1 = 3 + R A2 = 6, A3 = 18
It's also an equal ratio sequence
The common ratio is 3, so A1 = 2, r = - 1
It's easy to turn such a problem into a concrete quantity

1. The school bought 50 bundles of English exercise books and 50 bundles of mathematics exercise books. The number of bundles of the two kinds of exercise books is 3 / 10 of the total number of the two kinds of exercise books. How many bundles of oral exercise cards did you buy?
2. There are 147 pages in a story book. Xiao Gang read 2 / 7 of the whole book every day for two days. Which page should he read on the third day?
3. There are 150 bags of Huafeng instant noodles and 90 bags of Kangshifu instant noodles in the supermarket. After selling how many bags of Huafeng instant noodles, the number of the remaining bags of Huafeng instant noodles is exactly 7 / 9 of Kangshifu's?
4. Two ribbons of the same length. The first one takes 3 / 5, and the second one takes 3 / 5 meters. Which one of the remaining ribbons is longer?
5.18-3 and 8 / 9 =? (this is just a calculation problem.)

【1】 (50 + 50) × 3 / 10 = 30 bales
【2】 147 × 2 / 7 × 2 + 1 = 85 pages
【3】 150-90 × 7 / 9 = 80 bags
【4】 It can't be compared. When the length is 1 meter, the remaining one is the same length. When the length is larger than 1 meter, the remaining one is the same length
When it is less than 1 meter, the first one remains long
【5】 18-3-8 / 9 = 15-8 / 9 = 14 and 1 / 9
If you have any questions, you can go to Baidu Hi

As shown in the figure, in the isosceles trapezoid ABCD, ab ‖ CD, extend the bottom edge AB to e, so that be = DC

It is proved that connecting BD. ∵ ab ∥ CD, be = DC, ∵ quadrilateral becd is parallelogram, ∵ CE = BD, ∵ quadrilateral ABCD is isosceles trapezoid, ∵ AC = BD, ∵ AC = CE

1 () 2 () 3 () 4 () 5 () 6 () 7 = 1 fill in the operation symbol in the bracket

1（*）2（-）3（-）4（+）5（-）6（+）7=1

Why is the rank of the real symmetric matrix less than the order that the determinant of the matrix is equal to 0?
5 -1 3
-1 3 -3
3 - 3 C the rank of the matrix is known to be 2
But why is the determinant 0 when its rank is 2?

I suggest you take a closer look at the definition of matrix rank. For a real symmetric matrix of order 3, matrix rank means that it has at least one determinant of order 2 submatrix 0, while the determinant of order 3 submatrix, that is, the matrix itself, is 0