One day about 200 years ago, in a rural primary school in Brunswick, Germany, an arithmetic teacher was teaching students. The teacher from the city thinks he is lofty, so he goes so far to teach a group of silly children in the country. Therefore, he felt wronged, often lost his temper for no reason, and often reprimanded and flogged students. When the children saw a cat, they were scared like mice.

On this day, the arithmetic teacher was in a bad mood and walked into the classroom with a sad face. He said to the students in an orderly way, "Today, you gave me the sum of 1 plus 2, plus 3, plus 4 ... until 100. Anyone who is not good at it is not allowed to go home for dinner. " After that, he stared at the child like an evil spirit, then sat down in the chair and closed his eyes. The children were afraid and anxious, so they quickly took out the slate and calculated: 1+2=3, 3+3=6, 6+4= 10, 1 5 =15, ... Alas, this problem is really difficult to do, from/.

Just as everyone was busy cleaning the slate, I saw a boy stand up, walked to the teacher with a slate in his hand and whispered, "Teacher, I have worked it out. Is this the answer? " Without looking up, the arithmetic teacher waved and said, "Go! Let's go Let's go Even if it is so fast, it must be wrong! " The child stood still, and he pushed the slate forward again. "Have a look, teacher. I think this answer is correct. " The arithmetic teacher was about to have an attack, but when he looked up, he was surprised. The number "5050" is written on the slate. He calculated the answer in advance and the result was correct. However, it took him a long time to work out the problem. How did a 9-year-old get out so soon? He was a little surprised and asked, "How did you work it out?"

"Teacher, I didn't add them one by one in the order of 1 plus 2 plus 3. I looked at the formula carefully and found that in this addend of 100, the sum of two numbers at one end and one tail is 10 1. You see, 1+ 100 = in this way, a * * * has 5010, and 50 times1kloc-0/is 5050. "

"ouch! Why didn't I think of that? " The arithmetic teacher looked at the student in surprise. Indeed, he was greatly shocked. I didn't expect such smart people among rural children. You know, the method used by this child is the "arithmetic progression summation" method discovered by mathematicians after long-term research. Since then, teachers have been preparing lessons and listening carefully, and their attitude towards students has been greatly improved. Especially for this clever child, I gave enthusiastic help and careful guidance, which made him embark on the road of loving mathematics.

This clever boy is Gauss,