First, the price of color TV set was reduced by 20% and then by 25%. What's the price now

First, the price of color TV set was reduced by 20% and then by 25%. What's the price now

100% * (1-20%) * (1-25%) = 60% right, please accept

From natural numbers 1,2 , 2010, so that the sum of any three numbers can be divided by 21. Find the maximum value of n

In order to make any three numbers divisible by 21, the array must satisfy all 21 congruence, otherwise at least one group of sums can be found and cannot be divisible by 21
If the sum of three numbers can be divided by 21, then the remainder of 21 must be 0, 7 and 14
2010 / 21 = 95 …… fifteen
So we can get two groups
7 + 21 * k or 14 + 21 * k, respectively
k=0,1,2,…… ninety-five
The maximum value of n is 96

A mathematical problem of inequality in grade one of junior high school
A coin collector wants to change a 3.50 yuan note into coins with denominations of 1, 2 and 5 respectively. He requires that the total number of coins be 150. The number of 2-cent coins is not less than 20 and is a multiple of 4. 5-cent coins are more than 2-cent coins. Please design all the exchange schemes according to the above requirements

1=x 2=y 3=z
x+2y+5z=350
x+y+z=150
y>=20 z>y
When y = 20, z = 45, x = 85
y=24 z=44 x=82
y=28 z=43 x=79
y=32 z=42 x=76
y=36 z=41 x=73

7 / 8 kg represents (), 0.25 kg represents (), 25% represents ()

7 out of 8 kg means (7 out of 8 of 1 kg), 0.25 kg means (1 out of 4 kg), 25% means (1 out of 4 kg)

0.0000025 by scientific counting method

0.0000025=2.5×10ˉ6

It's questions 9 and 10 on page P71 of the eighth grade mathematics book of the people's education press,

9. ∵ the two sides of a triangle are equal, 88 = 88
L = the height of the base of the triangle
L ⊥ bottom edge
∴l²=88²-32² ∴l≈81.975
10. Let the height of water surface be x and the length of reed be x + 1
（X+1）²-X²＝（10／2）²
We get 2x + 1 = 25
X = 12

As shown in the figure, in the rectangle ABCD, ab = 10, BC = 12, point P is the midpoint of the edge of CD. Fold the rectangle ABCD so that point a coincides with point P, and point B falls at point G, then the length of crease EF is______ ．

Through point E, make em ⊥ BC at point m, ∵ fold rectangle ABCD, make point a coincide with point P, and point B falls at point G, ∵ 1 = ﹥ 4, ∵ 1 + ﹥ 2 = 90 °, ∵ 2 + ﹥ 3 = 90 °, ∵ 1 = ﹥ 3, ∵ EMF = 90 °, ∵ d = 90 °, ∵ ADP ∽ EMF, ∵ DPFM = ADEM, ∵ in rectangle ABCD, ab = 10, BC = 12, point P is the midpoint of CD side, ∵ ad = 12, DP = 5, ∵ 5mf = 1210, the solution is FM = 256, ∵ EM = a B = 10, EF = 102 + (256) 2 = 656

How to calculate 37.8 × 8.17-71.7 × 3.78 with a simple method

37.8×8.17－71.7 ×3.78
=37.8×(8.17－7.17 )
=37.8×1
=37.8

Chemistry in grade one of senior high school: Calculation of chemical reaction rate
In a 2 l closed container, 1 mol SO 2 and 1 mol O 2 are added, and the reaction is as follows: 2 SO 2 + O 2 = 2 so 3
When the reaction lasted for 10s, the amount of SO2 was 0.6mol
(1) What is the chemical reaction rate expressed by SO2?
(2) What is the chemical reaction rate expressed by SO3 or O2?

1. SO2 reduced by 1-0.6 = 0.4mol
4 / 2 = 0. 2mol / L
The reaction rate is C = △ C / T = 0.2/10 = 0.02 mol / L · min
The ratio of reaction rate is equal to the stoichiometric number
v(SO3)/2=0.02/2=v(O2)/1
v(SO3)=0.02mol/L·min
v(O2)=0.01mol/L·min

A triangle is equal to a parallelogram in height. It is known that the area of the parallelogram is 5 square meters larger than that of the triangle. What is the sum of the areas of the two figures?

15 square meters
Parallelogram and triangle have the same base and height. Let H be the height and X be the bottom
The area of a parallelogram is the base times the height, while a triangle is half the base times the height
We can know that the area of difference between them is the area of triangle
S＝hx－1／2hx＝1／2hx＝5
Their total area is 15 square meters