Find the law - 1.21.11.31.21.41. What are the next three numbers

Find the law - 1.21.11.31.21.41. What are the next three numbers

The next three numbers are 31.51.41

One half of a number is five more than two fifths. What's the number

50
Let the number be X
Then 1 / 2x = 2 / 5x + 5
1/10 x =5
x=50

The difference between a and B is one eighth. Two fifths of a is equal to one half of B. what is the sum of a and B

The ratio of two fifths of a to one half of B is 1 / 2:2 / 5 = 5:4
Because the difference between a and B is one eighth, their sum is 1 / 8 / (5-4) * (5 + 4) = 9 / 8

One half x-two thirds y = - two fifths x-three fifths 5Y = - Four Thirds of the solution of quadratic equation of two variables

1/2x-2/3y=-2/15
1/2x-5/3y=-3/4
The first minus the second gives y = 37 / 60
Y = 37 / 60 is substituted into any equation to get x = 5 / 9

Please write down the following three numbers. Can you name the 15th and 2010 numbers?
①-1,-2,+3,-4,-5,+6,-7,-8----------
②-1,1/2,-3,1/4,-5,1/6,-7,1/8------

① The 15th is + 15 and the 2010 is + 2010;
② - 9,1 / 10, - 11; the 15th is - 15 and the 2010 is 1 / 2010

Look at the numbers in the following column. Please write down the following three numbers. Can you name the 10th number, the 101st number and the 2004 number?
The first question: - 1, - 2, + 3, - 4, - 5, + 6, - 7, - 8, (), (), (). The second question: - 1, half, - 3, quarter, - 5, one sixth, - 7, one eighth
Find the rule: - 1 / 3,2 / 5, - 2 / 7,3 / 9, - 3 / 11 ()

+9 -10 -11 -101 +2004
-1 / 9-11-101 1 / 2 000
4/13 -4/15 5/17 -51/203 1003/4009

Look at the numbers listed in the following order. Please write down the following three numbers. Can you tell us what the 15th number, the 101st number and the 2011 number are
-1,-2,+3,-4,-5,+6,-7,-8,（ ),( ),( )

+9, - 10, - 11, the 15th is + 15, the 101st is - 101, and the 2011 is - 2011

Observe the following column of numbers to explore the law
－1,1/2,-1/3 ,1/4 ,－1/5 ……
(1) Fill in the number 7, 8 and 9
(2) What is the number 2004? If the number in this column is infinite, which number is closer to?

（1） -1/7,1/8,-1/9
（2） 1/2004
0

Observe the following two columns of numbers in order, what are their arrangement rules? Can you name the 48th, 101st and 2010 numbers of these two columns
（1）-1,1/2,-3,1/4,-5,1/6,-7,1/8,...
(2)1/2,0,-1/2 ,0,1/2,0,-1/2,0,...

(1) If the odd term is - N and the even term is 1 / N, there are 1 / 48, - 101 and 1 / 2010
(2) If the odd term is 1 / 2 and - 1 / 2 cycles, and the general term is 1 / 2 times {(- 1) [(n-1) / 2]}, then there are 0,1 / 2,0

The numbers of the following columns have certain regularity. Please write down the following three numbers according to the regularity, and find out the 15th, 100th and 101st numbers
0,-1,0,-1,0,-1,0,-1——,——,——.——,——,——.
-1,2,-3,4,-5,6,-7,8,——,——,——.——,——,——.
1,-1/3,1/5,-1/7,1/9,-1/11,1/13,-1/15,——,——,——.——,——,——.

For the first sequence, if the general term is an = 0 (when n = odd) and an = 1 (when n = even), then the 15th number is 0100 and - 1101 is 0
The second sequence, (I find that you may not understand the general term, and I will give you the answer directly) - 12 - 34 - 56 - 78 - 910 - 11, the 15th number is - 15, the 100th number is 100, and the 101st number is - 101
The third sequence is 1 - 1 / 3 1 / 5 - 1 / 7 1 / 9 - 1 / 11 1 / 13 - 1 / 15 1 / 17 - 1 / 19 1 / 21, the 15th is 1 / 29, the 100th is - 1 / 199, and the 101st is 1 / 201