The level of air quality is related to the amount of pollutants in the air. What can be used to express it? If the pollution index is 101-200, the air quality is

It can be expressed by pollution index, and the air quality is light pollution

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1. Example (1) 8*73+52*8 =8*（73+52） =8*125 =1000 Example (2) 9*96+3+9 =9*（96=3+1） =9*100 =900 For my daughter's homework, I don't know how to calculate, why to calculate like this, and why, exercises 1、 54 * 99 + 99 + 45 II. 54 + 99 * 99 + 45 3、 100 * 89 + 89 * 11 + 89 * 89 IV. 100 * 89-89 * 11-89 * 89 There is also the question 5*999+5+99*7+7+4*9+4=
2. The simple calculation is (53.76-17.6) △ 1.8 (0.8 × 7 + 4.56 △ 1.9) × 12.5 15.73-（2.17+0.73）-1.83
3. The expression of parabola y = ax ^ 2 + BX through D (4,3) a (6,0)
4. If a divided by B equals 45, then (a multiplied by 3) divided by B equals (), and a divided by (b multiplied by 3) equals (). Thank you,
5. Calculation formula of trapezoid circumference Circumference!
6. How much is a multiplied by its reciprocal and a equals one and four fifths
7. What is the solution of equation 3 / (x-1) + 4x / (1 + X & sup2;) = - 1 / (x + 1) and how to solve this equation?
8. Fill in the blanks: 1 / 6, 1 / 4, 3 / 8, (), (), 81 / 64
9. When m takes what value, the solution of the equation 4x + m (X-6) = 2 (2 + 3M) about X is a positive integer Attention! It's 2 + 3M, not 2-3m
10. Simple calculation of 2000 × 19991999-1999 × 20002000 Try to finish on the same day! Don't copy!
11. The story about mathematics is less than 20 words! Within 100 words!
12. How many days are there from October 24, 2010 to today
13. Simple calculation by factorization （1）22.4^2-27.6^2 （2）2.03*2.5+4.83*2.5+3.14*2.5 （3）1.25*14^2-125*8.6^2 （4）102^2-2*(100^2-2^2)+98^2 （5）27*1.8^2-12*1.2^2 （6）(1-1/2^2)(1-1/3^2)(1-1/4^2)…… (1-1/2008^2)
14. If we keep fixed points F1 (- 2,0) and F2 (2,0), then the locus of the moving point P satisfying the following conditions in the plane is hyperbolic A./PF1/-/PF2/=_ +3 B./PF1/-/PF2/=_ +4 C./PF1/-/PF2/=_ +5 D./PF1/^2-/PF2/^2=_ +4 Note: Pf1 / medium / is absolute value_ +3 is positive and negative
15. It is known that 2x + y = 7 is a quadratic equation of X and y, and the solutions of the equations are positive integers
16. Given that point a (0, - 1) and point B are moving points on the curve X ^ 2-y ^ 2 + X + 2Y + 3 = 0, then the trajectory equation of the midpoint of line AB is obtained
17. What is the temperature of 4.2K
18. 16 π of the angle is reduced to α + 2K π (K ∈ Z 0)
19. The form of - 1125 ° to 2K π + α (K ∈ Z, 0 ≤ α < 2 π) is () A. −6π−π4B. −6π+7π4C. −8π−π4D. −8π+7π4
20. The following angles are reduced to 0 to 2 π plus 2K π (K ∈ z) (1) -25/6π (2)-5π (3)-45° (4)400°