The unknown term X: 12.5 = 1 / 4 0.3: x = 4 / 9

The unknown term X: 12.5 = 1 / 4 0.3: x = 4 / 9

Hello, colorful sky 1
x：12.5=1/4
4x=12.5
x=12.5/4
x=3.125
0.3：x=4/9
4x=0.3×9
4x=2.7
x=2.7/4
x=0.675
Analysis: the product of the outer term of the ratio is equal to the product of the inner term

Xiao Ming calculated 20 questions, and stipulated that if he did one right question, he would get 5 points, and if he did one wrong question, he would get 3 points. As a result, Xiao Ming did all 20 questions, but only got 60 points, and asked him to do it right______ Question

20 - (100-60) △ 5 + 3, = 20-40 △ 8, = 20-5, = 15 (question); answer: he did 15 questions correctly, so the answer is: 15

Xiaodong calculates 20 questions, and 3 points will be deducted for one wrong question. If Xiaodong scores 60, how many questions did he do right?

5x-3y=60
x+y=20
x=15

Given 3a-6b-5 = 0, find 2a-4b = 2008
It's today's assignment, first aid~

According to known
3a-6b-5 = 0 is transformed into 3 (a-2b) = 5
Namely: a-2b = 5 / 3
So 2a-4b + 2008 can be converted into
2(A-2B)+2008=2*5/3+2008=10/3+2008=6034/3

Nine numbers and nine squares add horizontally and vertically to make one number

159
six hundred and seventy-two
eight hundred and thirty-four

2x-3y = 4, 5x-3y = 19,

2x--3y=4 (1)
5x--3y=19 (2)
(2) - (1)
3x=15
x=5
Substituting x = 5 into (1), we get the following result:
2x5--3y=4
--3y=--6
y=2
So the solution of the original equations is: x = 5
y=2.

Simple calculation of 1996 + 1997 + 1998 + 1999 + 2000 + 2001 + 2002

Method 1
Take an approximate mean value, such as 2000
There are 7 easy to see numbers. Subtract 2000 from each number, and the difference is as follows:
-4,-3,-2,...,2
From - 2 to 2, the sum is 0
The results are as follows
2000*7-4-3=13993
Method 2
Obviously, these numbers form an arithmetic sequence
So the mean value of the first and last two numbers is the mean value of all numbers
The average value is: (1996 + 2002) / 2 = 1999
There are 7 easy to see figures from 2002 to 1996
1999*7=(2000-1)*7=14000-7=13993

Let n be any integer, and use the algebraic expression containing n to represent any odd or even number

The multiple of 2 of any integer represents an even number, which is 1 or more less than the multiple of 2 of an integer. The number of 1 is odd, and because the number is generally divided into positive and negative integers, the answer is ± 2n (even number) and ± (2n-1) (generally speaking, odd numbers are expressed in the form of - 1, and positive and negative 2n + 1 can also be used)!

1479-399 calculated by simple method

1479-399 =1479-400+1=1079+1=1080

The base of the triangle is 5.6CM long. Lengthen its lower side by 2cm and increase its area by 5cm

Height: 5 × 2 △ 2 = 5cm
Original area: 5.6 × 5 △ 2 = 14 square centimeters