Math 1 + 3 + 5 + 7 + 9. + 199 = what's the square Do me a favor, find the law, 1 = 1 square, 1 + 3 = 2 square, 1 + 3 + 5 = 3 square

Math 1 + 3 + 5 + 7 + 9. + 199 = what's the square Do me a favor, find the law, 1 = 1 square, 1 + 3 = 2 square, 1 + 3 + 5 = 3 square

The sum of n odd numbers = the square of n
1 = the square of 1
The square of 1 + 3 = 2
1 + 3 + 5 = the square of 3
.
1 + 3 + 5 + 7. + (2n-1) = the square of n
1+3+5+7+9.+199=100^2
Xiao Li read a story book. On the first day, she read 25% of the whole book. On the second day, she read 10 more pages than on the first day, and there were 30 pages left. This book is not very good
Suppose the book has x pages
x/4+(x/4+10)+30=x
x/2+40=x
x/2=40
X = 80 pages
A: the book has 80 pages
To teach a math problem, we should calculate it skillfully
999x999 =? Skillful calculation, formula
999x999=999x（1000-1）=999000-999
999x999=999×(1000-1)
=999000-999
=998001
(1000-1)×（1000-1）=1000000-1000-1000+1=998001
1000×999－1×999*^_ ^
The equation can be established by filling the 9 numbers 1, 2, 3, 4, 5, 6, 7, 8 and 9 in the box of the following equation respectively. (hint: 3634 decomposition quality factor)
( )( )x( )( )=( )( )x( )( )( )=3634
46×79=23×158=3634
Xiao Li read a story book. She read 19 pages on the first day, 17 pages on the second day, and there were 33 pages left. What percentage of the book did she read and what percentage did she not read
Today is the day
19+17+33=69
Seen: 19 + 17 = 36 36 △ 69 = 69 / 36 = 23 / 12
Unseen: 1-23 / 12 = 23 / 11
A: 23 / 12 of the books have been read and 23 / 11 of the books have not been read
for instance:
1 ton of coal is 750 Jin of pure coal after moisture removal. Now there are 21.6 tons of pure coal. How much is the weight before moisture removal
I tried 21.6 divided by 0.75 to get it, but why divided by 0.75 is not clear 3Q
1 ton = 1000 kg = 2000 Jin
If you want to check it, you should check it
It's very simple! Because 750 Jin = 0.75 ton
Put the nine numbers 1, 2, 3, 4, 5, 6, 7, 8, 9 in the box to make the equation hold. How many different ways can you think of? □□□=12×□□□=13×□□□
According to the stem analysis, 327 = 12 × 654 = 13 × 981, or 273 = 12 × 546 = 13819
Xiao Li read a 120 page story book. She read 1 / 5 of the whole book on the first day and 1 / 2 of the whole book on the second day. How many pages are left?
120*（1-1/5-1/2）=36
36 pages
120-120 / 5-120 / 2 = 36 pages
120-120X1/5-120X1/2= 36
A
120-120*(1/5+1/2)=120-84=36
Thirty-six
Solving a math problem
Now my account balance is 689, every day I can get 5 yuan more than yesterday, today is the 34th day Please, I'll have 10000 yuan in my account in a few days I wish her a lifetime
If you set up an account for another n days, you will get 10000 yuan
689＋（698＋5）＋〔（689＋5）＋5〕＋｛〔（689＋5）＋5〕＋5｝＋……
＝689n+〔5+2×5＋3×5＋…… (n-1)×5〕
＝689n+5×〔1+2＋3＋…… (n-1)〕
＝689n+5×(1+n-1)(n-1)/2
＝689n+5×n(n-1)/2
＝10000
1378n+5n(n-1)=20000
5n^2+1373n-20000=0
86 days = 14 days
So in 14 days, there will be 10000 yuan in the account
Put the nine numbers 1, 2, 3, 4, 5, 6, 7, 8, 9 in the box to make the equation hold. How many different ways can you think of? □□□=12×□□□=13×□□□
According to the stem analysis, 327 = 12 × 654 = 13 × 981, or 273 = 12 × 546 = 13819