Before paragraph time, we learned prime number and join several one class. The teacher is known clearly to let us prime number differs with what join number, can be elaborative really!
前段时间，我们学习了质数与合数一课。老师为了让我们清楚地认识质数与合数的不同，可真是煞费苦心啊！
On the class, the teacher guided us to know prime number and join number. Prime number weighs prime number again, its factor has and have two only, it is to be mixed respectively it this full marks / personally, and join number besides one still have other factor with itself. That is to say, prime number has two factor only, and add up to number to have 3 factor at least.
课上，老师引导我们认识了质数与合数。质数又称素数，它的因数有且只有两个，分别是一和它本满分/身，而合数除了一和它本身还有别的因数。也就是说，质数只有两个因数，而合数至少有三个因数。
Be in blame 0 natural in, besides have prime number and join number (the factor that counts by several classification) , still have a very special number, this number has a factor only, and it is itself, right, namely " 1 " . "1 " both neither is prime number, also not be to join number, so very special.
在非零自然数中，除了有质数和合数（按一个数的因数个数分类），还有一个十分特殊的数，这个数只有一个因数，且是它本身，没错，就是“1”。“1”既不是质数，也不是合数，所以十分特殊。
In the class, the teacher still made us seasonable do relevant exercise in school work, know newly with helping us consolidate. After the class, the teacher guides us how to find out prime number quickly further. Below the teacher's be good at teaching, we knew 2, 3, 5, the multiple of 7 (besides their itself) , it is to join number; Even besides " 2 " it is to join number; Odd and differ it is prime number surely; The smallest prime number is " 2 " , the smallest joining number is " 4 " , mix without the largest prime number join number; Going up is 2, 4, 6, 8, 0 or the much digit of 5 is to join number; Each are digital go up mixing is " 3 " diploid much digit also is to join number; Going up is 1, 3, 5, the number of 7 may be prime number.
在课中，老师还让我们及时做了相关的习题，以帮我们巩固新知。课后，老师进一步引导我们如何更快地找出质数。在老师的循循善诱下，我们知道了2、3、5、7的倍数（除了它们本身），都是合数；偶数除了“2”都是合数；奇数不一定是质数；最小的质数是“2”，最小的合数是“4”，没有最大的质数和合数；个位上是2、4、6、8、0或5的多位数是合数；各数位上的和是“3”的倍数的多位数也是合数；个位上是1、3、5、7的数可能是质数。
Teacher not only such, when becoming a problem to let us can more apace judgement prime number and join number, still let us bear the prime number watch of 100 less than. Finally, the teacher goes to the lavatory to let us remember, teach us an a pithy formula again:
老师不仅如此，为了让我们做题时能更快速地判断质数与合数，还让我们背了100以内的质数表。最后，老师为了让我们记忆方便，又教给我们一个口诀：
2357 with 11,
二三五七和十一，
13 from the back be seventeen.
十三后面是十七。
Nine million nine hundred and twenty-three thousand one hundred and ninety-nine,
十九二三二十九，
Three million one hundred and thirty-seven thousand three hundred and ninety-one.
三一三七四十一。
Four million three hundred and forty-seven thousand four hundred and ninety-three,
四三四七五十三，
Five million nine hundred and sixty-one thousand five hundred and ninety-seven.
五九六一六十七。
July 1 seventy-three thousand six hundred and ninety-nine,
七一七三七十九，
Eight million three hundred and eighty-nine thousand eight hundred and ninety-seven.
八三八九九十七。
In the teacher attentive explain, use heart guiding, patience to correct, I do not lose popular confidence eventually, knew these two truly " friend " , I remembered, also be carried on the back, my achievement feeling increased again.
在老师的细心讲解、用心引导、耐心纠正下，我终于不负众望，真正认识了这两位“朋友”，我记住了，也背下来了，我的成就感又增加了。(文/黄烨)
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