Calculate 3 / 10 × 11 + 3 / 11 × 12 + 3 / 12 × 13 +. + 3 / 19 × 20

Calculate 3 / 10 × 11 + 3 / 11 × 12 + 3 / 12 × 13 +. + 3 / 19 × 20

Spend half a day trying to answer questions, the landlord line also ignored
The quality of the answer is another matter. There is no basic politeness
In regret

-3-4 + 19-11 - four and two thirds + one and twelve eleven -- Seventeen and one fourth -- two and eighteen seventeen
-3-4 + 19-11 - four and two thirds + one and twelve eleven -- Seventeen and one fourth -- two and eighteen seventeen

3-4+19-11=（3+19）-（4+11）=22-15=7
(4+2/3)+(1+11/12)-(17+1/4)-(2+17/18)
=(4+2/3)+(2-1/12)-(17+1/4)-(3-1/18)
=（4+2-17-3）+（2/3-1/12-1/4+1/18）
=-14+（8/12-1/12-3/12+1/18）
=-14+（1/3+1/18）
=-14+（6/18+1/18)
=-14+7/18
=-13 and 11 / 18

How much is 1 in 10 plus 1 in 11
With explanation

Such a question, the more simplified the algorithm, the more inaccurate the answer
I give a simpler approximation algorithm, but only one significant number can be guaranteed
This sequence is a bit of an arithmetic sequence
1 / 12 is the middle of the first five numbers, so suppose it is the average of the first five numbers, so the sum of the first five numbers is 5 / 12
Similarly, 5 / 17 is the sum of the last five numbers
So the answer = 5 / 12 + 5 / 17 is about 0.7

How to calculate easily?

0.19÷4/5-1.25x0.71
=0.19*5/4-1.25*0.71
=1.25*(0.19-0.71)
=-1.25*0.52
=-1.25*0.8*0.65
=-0.65

If there are three continuous natural numbers, the smallest one is n, then the average of the three numbers is ()
A. 3nB. 2nC. n+1D. n-1

Because three continuous natural numbers, the smallest of which is n, then the other two are: n + 1, N + 2, (n + 2 + N + 1 + n) △ 3, = [(n + 1) × 3] △ 3, = n + 1; so choose: C

Three continuous natural numbers, the smallest number is a, what is the largest number? What is the average of these three numbers?

Three continuous natural numbers, the smallest number is a, the largest number is a + 2, the average of these three numbers is a + 1

Put the natural numbers 1, 2, 3 99 is divided into three groups. If the average of each group is exactly equal, then the three averages are exactly equal, the three averages are equal
What is the sum of the two

Because 1 + 2 + 3 +. + 99 = 4950
Divided into three groups: 4950 / 3 = 1650 (sum of each group)
There are 33 numbers in each group, the average is 1650 / 33 = 50
Sum of three means = 50 + 50 + 50 = 150

Put the natural numbers 1, 2, 3 99 is divided into three groups. If the average of each group is exactly equal, then the product of the three means is______ ．

Let the average number of each group be x, then 33x + 33x + 33x = 1 + 2 + 3 + +99, that is, 99x = (1 + 99) × 99 △ 299x = 99 × 50, x = 50. So the product of the three averages is 503 = 125000. So fill in 125000

Put the natural numbers 1, 2, 3 998999 is divided into three groups. If the average of each group is exactly equal, then the sum of the three averages is______ ．

1+2+3+… +998 + 999 = (1 + 999) × 999 △ 2 = 500 × 999, the sum of each group is: 500 × 999 △ 3 = 500 × 333, the average of each group is: 500 × 333 △ 333 = 500, then the sum of the average of the three groups is: 500 × 3 = 1500 answer: the sum of the three average is 1500, so the answer is: 1500

Put the natural numbers 1, 2, 3 998999 is divided into three groups. If the average of each group is exactly equal, then the sum of the three averages is______ ．

1+2+3+… +998 + 999 = (1 + 999) × 999 △ 2 = 500 × 999, the sum of each group is: 500 × 999 △ 3 = 500 × 333, the average of each group is: 500 × 333 △ 333 = 500, then the sum of the average of the three groups is: 500 × 3 = 1500 answer: the sum of the three average is 1500, so the answer is: 1500