There was a theft in the street. The thief was so cunning that he didn't leave any clues at the scene, but the money in the safe was gone. How did the thief know the password? Conan found a small piece of paper at the scene with four numbers written on it: 1008, 1260, 1386, 1 134. But the password can only be three digits. What does it have to do with these four numbers? Suddenly Conan's mind flashed. He did a quick calculation, then pressed three numbers on the safe, and the safe was opened. Do you know the password? How did you get it?

The answer is1+8 =1+2+6 =1+0+3+4 = 91+3+8+6 =18.

There are three times as many apple trees as pear trees in the orchard. Master Lao Wang fertilizes 50 apple trees and 20 pear trees every day. A few days later, all the pear trees were fertilized, but 80 apple trees were not fertilized. Excuse me: How many apple trees and pear trees are there in the orchard? I am not intimidated by this question, but it can stimulate my interest. I think the apple tree is three times as big as the pear tree. If two kinds of trees are to be fertilized on the same day, Master Lao Wang will fertilize "20×3" apple trees and 20 pear trees every day. In fact, he only fertilizes 50 apple trees every day, which is 10, and the last 80 trees. Therefore, Master Lao Wang has been fertilizing for 8 days. 20 pear trees a day, 8 days is 160 pear trees. According to the first condition, there are 480 apple trees. This is to solve the problem with the idea of hypothesis, so I think the hypothesis method is really a good solution.

3. The origin of Arabic numerals

Xiaoming is a child who likes to ask questions. One day, he became interested in the numbers 0-9: Why is it called "Arabic numerals"?

So he asked his mother, who was a math teacher, "Since 0-9 is called Arabic numerals, it must have been invented by Arabs?"

Mom shook her head and said, "Arabic numerals were actually invented by Indians." About 1500 years ago, Indians used a special word to represent numbers. There are 10 words, and you can write both strokes. Later, due to contacts between countries, these figures were introduced into Arabia. Arabs thought they were very simple, so they began to use them widely in their own countries and spread throughout Europe. In this way, they gradually became the numbers we use today. Because Arabs have played a great role in the spread of this number, people are used to calling this number' Arabic number'. "

Xiao Ming said happily, "So that's it. Mom, can this be called' making a mistake'? " Xiao Ming and his mother both laughed.