Answer: weigh three first, then take one, and then calculate the difference after weighing.
2. Someone walked 32 kilometers north and then 36 kilometers south, and asked which of the following might be correct.
He is 4 kilometers away from the starting point. He is more than 48 kilometers away from the starting point. He is 68 kilometers away from the starting point. He is less than 4 kilometers away from the starting point. He is more than 4 kilometers away from the starting point, but less than 68 kilometers away.
A: 1, 3, 5
Every page of Xiao Ming's diary is marked with numbers. He uses the number ***98 1 from 0 to 9. How many pages does this diary have?
A: 357
Xiaohua took part in the motorcycle race, and the number of participants was as large as the number of participants. Any two athletes meet only in one game, and four people appear in each game. He asked * * * how many people attended.
A: 13
5. There are nine numbers (1~9) to form two numbers (each number is used only once). What's the biggest digital product?
Answer: 9642 8753 1
6, one hundred steamed buns and one hundred monks, three big monks are even less controversial (that is to say, three big monks each eat three steamed buns), three small monks are divided into one, and how many monks are there? (Excerpted from Cheng Dawei's Arithmetic Unity in Ming Dynasty)
Answer: 1 monk and 3 monks are regarded as 1 group, and 100 monks can be divided into 100/4=25 (group).
Because each group has 1 monk, there are 1*25=25 monks (people).
So there was the little monk 100-25=75 (person)
7. It takes three weeks and three days for three people to finish a job. According to this calculation, how long will it take four people to finish the work? (From 1997 Long Island Primary School Mathematics Competition in new york, USA)
A: It takes three weeks and three days for three people to finish a job. If 1 person finishes a job, it will take three times as many days as before: (3*7+3)*3=72 days.
If four people finish a job, it takes a quarter of 72 days: 72/4= 18 (days).
8. A book has 500 pages, numbered 1, 2, 3 ...1* * How many times has this number appeared? (From the "Primary Mathematics Olympics" exam in the United States)
Answer: 1~99 can be divided into ten groups: 1~9,10/9, 20 ~ 29...90 ~ 99, 10~ 19 except. So 1 1+9=20 (times) appears.
From 100 to 199, compared with the previous paragraph, there are 1 00 times for "1" in hundreds, but the situation of "1"in units and tens is the same as the previous paragraph. So there is 100+20= 120 (times).
There is no "1" in the 100 in the third segment of 200~299, 300~399 and 400~499, but the situation of "1" in the single digit and the tenth segment is the same as that in the 1~99 segment, with 20 times each. So 20*3=60 (times)
1 will not appear in 500.
To sum up, the total frequency of * * * is 20+ 120+60=200 (times).
9. Father and son set out from both directions at the same time, with a distance of 10 km. Father walks 6 kilometers per hour and son walks 4 kilometers per hour. Dad brought a puppy. The puppy ran to his son at the speed of 10 km per hour. When he meets his son or father, he immediately turns around until the father and son meet. How many miles did the dog run?
A: The time for the puppy to run is the time for the father and son to walk.
It took father and son to meet: 10/(6+4)= 1 (hours).
So the puppy ran 1 hour, 10 km.
10 When an old man died, he left 17 horses to his three sons, saying that the eldest brother had half, the second one third and the third one ninth, and it was forbidden to kill horses. How to divide it?
Answer: If you borrow a horse, you will get 18. The boss got 9 horses, the second got 6 horses, and the third got 2 horses, which added up to 17 horses, and the remaining one was returned.