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48 boards, 3.5 long and 0.25 wide 4.4 long, 0.3m wide, how many boards do you need!
We need x boards
4.4*0.3*x=3.5*0.25*48
The solution is: x = 32 (approximate)
A: 32 boards are needed
A simple algorithm of 1 / 2 + 1 / 2 △ 3 + 1 / 3 △ 4 +. + 1 / 9 △ 10
1/2+1/2÷3+1/3÷4+.+1/9÷10
=1/(1×2)+1/(2×3)+1/(3×4)+ --- +1/(9×10)
=1/1-1/2+1/2-1/3+1/3-1/4+ --- +1/8-1/9+1/9-1/10
=1-1/10
=9/10
1 / (2 × 4) + 1 / (4 × 6) + 1 / (6 × 8) + 1 / (8 × 10) + ···· + 1 / (2008 × 2010),
The original formula is 1 / 4 {4 × 1 / (2 × 4) + 4 × 1 / (4 × 6) + 4×1/2008×2010}
=1/4{1/1×2+1/2×3+…… 1/1004×1005}
=1/4×（1004/1005）
=251/1005
Explain
4×1/（2×4）+4×1/（4×6）+…… 4 × 1 / 2008 × 2010 divides 4 into 2 × 2 and two even dividers of denominator respectively
{1/1×2+1/2×3+…… 1 / 1004 × 1005} This is very familiar with N / N + 1
How to write an applied problem of solving equation in Mathematics in grade one of junior high school?
The first digit of a 4-digit number is 7. If the first digit is placed on a single digit, the new 4-digit number will be 3 more than half of the original 4-digit number. How to find the original 4-digit number?
There should be solutions and equations
Let the last three digits of this four digit number be X,
The original four digit number is 7000 + X,
The new four digit number is 10x + 7,
0.5×（7000+x）+3＝10x+7
3500+0.5x+3＝10x+7
9.5x＝3496
x＝368
The original four digit number was 7368
In a square with a circumference of 40 decimeters, make the largest circle. How many square decimeters is the area of this circle?
The radius of the circle is: 40 △ 4 △ 2 = 5 (decimeter). The area of the largest circle is: 3.14 × 52 = 78.5 (square decimeter). A: the area of this circle is 78.5 square decimeter
Given | a | = 2, | B | = 4, a > b, AB < 0, find the value of - 2ab-2a + 2B
|a|=2,|b|=4,a＞b,ab＜0
So a = 2, B = - 4
-2ab-2a+2b
= 16-4-8
=4
Mathematics practical problems of grade 6 (area of circle)
1. For a ring-shaped part, the inner diameter is 8cm and the outer diameter is 12cm. What is the area of the part in square centimeter?
2. The radius of the circular bottom of the TV Tower is 15m. Now we need to plant a 5m wide circular lawn around it. ① what is the area of the lawn? ② if 50 yuan is needed for each square meter of lawn, how much will it cost at least to plant this lawn?
1. A ring part, the inner diameter is 8cm, the outer diameter is 12cm. What's the area of this part in square centimeter? (12 △ 2) × (12 △ 2) × 3.14 - (8 △ 2) × (8 △ 2) × 3.14 = 62.8square centimeter. 2. The circular bottom radius of TV Tower is 15m, now we need to plant 5m wide ring grass around it
The area of a rectangle is 2.6 square meters, and that of a square is 2 and 25 / 14 square meters. Which figure has a larger area?
2+14/25=2.56
It is known that the time for sunlight to irradiate the earth is 8 minutes and 20 seconds, and the gravitational constant is 6.67 × 10-11 Nm2 / kg2. Try to estimate the mass of the sun (keep a significant number)
The distance between the earth and the sun r = (8 * 60 + 20) seconds * 3 * 10 ^ 8 m / S = 1.5 * 10 ^ 11 m, the earth's revolution cycle T = 1 year = 365 * 24 * 3600 seconds = 3.15 * 10 ^ 7 seconds, the centripetal acceleration of the earth's revolution = the gravitational acceleration of the sun to the earth, the centripetal acceleration a = (2 * pi * r / T) ^ 2 / r = 4Pi ^ 2 * r / T ^ 2, the gravitational acceleration plus
Application of physical sound phenomenon
If a speaker vibrates 5000 times, what is the frequency of the speaker? If the speaker is 68m away from you, how long does it take for you to hear the sound? (sound speed is 340m / s)
The frequency is 5000mz
The time is 68 / 340 = 0.2 seconds
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