Calculate the area and volume of all figures,

1. The perimeter of rectangle = (length + width) × 2 C = (a + b) × 2 2, the perimeter of square = side length × 4 C = 4A 3, the area of rectangle = length × width s = AB 4, the area of square = side length × side length s = A.A = a 5, the area of triangle = bottom × height △ 2 s = ah △ 2 6, the area of parallelogram = bottom × height s = ah 7

A mathematical problem about unit 1
For example: A is two-thirds of B, who is unit one? In short, there are many, the more the better! The most reward, but also a little difficult! Not too simple, but also additional answers, otherwise I don't know if I'm right!
Can also talk about how you find a unit, what tips? He who writes the secret can still get a reward,
What I said about "a is two-thirds of B, who is unit one" is just an example! You don't have to answer!

There are various ways to find unit 1
Personal summary: 2 points
1. For example, a is two-thirds of B and B is unit one
2. A constant quantity is regarded as unit 1
These two methods to learn, unit 1 problem to do up no problem

There are 17 natural numbers, the average of which is 21.3 to the first digit after the decimal point, so how many to the third digit after the decimal point?

21.3 × 17 = 362.1; so the sum of 17 numbers is: 362; 362 △ 17 ≈ 21.294; answer: the three digits after the decimal point is 21.294

In the speech contest of class 1, grade 6, when a boy gives a speech on stage, the number of boys is 45% of the number of girls. When a girl gives a speech on stage, the number of boys is only 78% of the number of girls. How many students are there in class 6 (1) of this school?

Suppose that there are x girls (x-1) × 78 = 45x + 1 & nbsp; 78x-78 + 78 = 45x + 1 + 78 & nbsp; & nbsp; 78x-45x = 45x + 178-45x & nbsp; 340x ／ 340 = 178 ／ 340 & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; X = 2525 × 45 + 1 = 20 + 1 = 21 (people) 25 + 21 = 46 (people). A: there are 46 students in class 6 (1) of this school

Calculate the area and volume of all figures,