巧解1/4>( )>1/5

1/4>( )>1/5,这类题目常见。一些资料都是把分数化成同分母分数或是同分子分数进行比较,然后得出答案。这种解法学生虽然能够理解和掌握,但较麻烦,特别是要填的空多了就更麻烦。 这里介绍一种既简便,又容易被学生理解和掌握的方法。如:     

“1/4>□/□>1/5”填法之我见

小学《数学》第十册第１２０页有这样一道真空题：　　。一般人们常用的是下面两种解法。 解法１：先化成同分母分数,将　与　通分,取公分母４０,则　＝　,　＝　,取中间数　,定有　＞　＞　。解法２：先化成同分子分数：　＝　,　＝　,取中间数　,定有　＞　＞　。 除以上两种一般解法外,我还总结出下面几种方法,并且比较简便。 解法１：取　与　的平均数,得 （　＋　）÷２＝　×　＝　 　　＞　＞ 解法２：把分数化成小数,得： 　＝０．０５,　＝０．２,取０．２４,必有　＞０． ２４＞　。 因为０．２４＝　,所以　＞…     

使学生相信1/4>1/5的教学安排

读了《湖南教育》1988年第10期贺大国同志撰写的课例征评——《为什么学生不相信‘1/4>1/5’》一文,我认为学生不相信1/4>1/5的主要原因,是教师忽视了对小学生心理特征的分析。那么,怎样才能使学生相信1/4>1/5呢?我以为,教学应作如下的安排。 1.结合学生的生活实际,引入平均分与份数的概念。如问:①8本图书平均分给 4个人,每人得几本?8本图书平均分给2个人,每人得几本?怎么     

Aerobasics — An introduction to aeronautics 12. Safety in aviation

Public awareness of airplane safety is very high due to the spectacular nature of airplane accidents. Partly as a result, civil airplane operations are tightly regulated at all levels from design to operation and maintenance. Scheduled airline operations have thus been able achieve a very high level of safety. In this article we quantify the safety of flight operations and indicate the design concepts like fail safety and safe life used in achieving a high level of safety. As an illustration, we consider the safety of a flight of a twin engine airplane in the event of one engine failure.     

Aerobasics — An introduction to aeronautics 14. Air navigation principles

Air navigation has evolved over the last hundred years from an art into a mature science. Airplane accidents due to navigational errors are practically nonexistent. In large measure this advance has been due to radio aids to navigation which operate under all weather conditions. However in remote areas and in hostile airspaces, the radio aids may not be available and a fully self contained navigational device is required. Navigation by stars (celestial navigation) is feasible under such conditions. But the inertial navigation system (INS) is the preferred choice. In recent times, a navigational instrument based on radio communication with specially designed satellites in low Earth orbits called the global positioning system (GPS) has become popular. This article deals with the principles of these various methods of air navigation.     

Aerobasics — An introduction to aeronautics 15. Mini and micro airplanes

There is much current interest in small unmanned airplanes weighing about five kilograms all the way down to about 100 grams. Even such small airplanes are capable of performing useful surveillance missions in peace time and during conflicts. As these airplanes operate at very low flight speeds in the range of about 10–20 m/s, their performance is strongly affected by the low Reynolds numbers characteristic of such flight. In this article, we consider the special aerodynamic and propulsion problems associated with the flight of such small airplanes.     

为什么学生不相信“1/4>1/5”?

一教师教学通用六年制七册91面“比较两个分数的大小”时,先组织学生复习“分数初步认识”中的内容,并读写下列分数:1/4,2/4,…,1/5,2/5,…,1/6,2/6,…,1/8,2/8,…。接着,(?)给学生每人一张卡片(卡片内容如下),要求他们在卡片上的每个图