2. The number should be (2.88-2.54)× 10=3.4 and the correct answer should be 5.94.
3. Method 1: Countdown
? Before the 10 pass: (2- 1)×2=2.
? Before the ninth pass: (2- 1)×2=2.
......
? So what? There were two at first.
Method ⅱ, equation method, too much trouble, suggested usage ⅰ.
4. (Now the questions of primary school students are wonderful and a bit tricky-? -)
Perform the following analysis:
No matter what you think,
If it's time for the other party to take it,
With two coins left, he took 1 and I lost.
When there were three coins left, he took two and I lost.
When there were five coins left, he took four and I lost.
But when there are four coins left, no matter how he takes them, he can't win.
That's him taking 1, and I'll take 2.
He takes two and I take 1.
He lost when he got four!
So the secret of winning is to find a way to leave four coins for each other!
Suppose I take it first,
If I take 1 first and the opponent takes 2, I can't leave him four coins at this time, and then I will lose anyway.
If I take two coins first and the other person takes four, then he will leave me four coins, and then no matter how I take them, I will lose.
If I take four coins first and the other person takes two, then he will leave me four coins, and then no matter how I take them, I will lose.
So the person who takes it first will definitely lose!
So the way to win is:
Take the coin later!
A. If the opponent takes 1, I will take 2.
A. After that, if the opponent takes 1 piece, I will take 2 pieces and leave 4 coins for him, so I will win in the end.
B. After that, if my opponent takes 2 pieces, I will take 1 piece and leave him 4 coins, so I will win in the end.
C. After that, if my opponent takes 4 pieces, I will take 2 pieces and leave him the last 1 coin, so that I can finally win.
B. If my opponent takes 2 pieces, I will take 4 pieces directly and leave him 4 coins, so I will win in the end.
C. If my opponent takes four, I will take two directly and leave him four coins, so I will win in the end.
5.-? Poor student.
I want to know whether those two diagonal lines are parallel, otherwise I can't do it, I can only work out the range of values.
Well, suppose they are parallel.
The red pen is the auxiliary line I made.
Sister has been doing it for a long time, and there may be a calculation error (unlikely). I hope you can think more about it in the future and try to do it independently, although it's difficult- -。
I hope this helps.