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公分母复习

复习怎么寻找公分母, 并且做一些练习题.

公分母

不同分数的分母相同,那么它们有 公分母.
运用公分母可以方便分数间进行比较和加减法运算.

寻找公分母

要找出两个(或多个) 分数的公分母,方法之一是列出各个分母的倍数,找到他们共有的最小倍数(最小公倍数).
例题
找出 start fraction, 7, divided by, 8, end fractionstart fraction, 3, divided by, 10, end fraction的公分母.
分母分别是 810,列出它们各自的倍数:
8的倍数:8, comma, 16, comma, 24, comma, 32, comma, start color #11accd, 40, end color #11accd, comma, 48, comma, 56, comma, 64, comma, 72, comma, start color #11accd, 80, end color #11accd, point, point, point, point, point, point
10的倍数:10, comma, 20, comma, 30, comma, start color #11accd, 40, end color #11accd, comma, 50, comma, 60, comma, 70, comma, start color #11accd, 80, end color #11accd, comma, 90, comma, 100, point, point, point, point, point, point
start color #11accd, 40, end color #11accdstart color #11accd, 80, end color #11accd 都是 810共同的倍数,都可以用作公分母.但是我们通常使用最小公倍数进行运算, 因为计算时数字越大越容易出错.
因此用start color #11accd, 40, end color #11accd 作为公分母.

通分

start color #11accd, 40, end color #11accd为公分母,把 start fraction, 7, divided by, 8, end fractionstart fraction, 3, divided by, 10, end fraction 通分.
先算出原来两个分数的分母分别乘以几可以得到start color #11accd, 40, end color #11accd
start fraction, 7, divided by, 8, end fraction, times, start fraction, divided by, 5, end fraction, equals, start fraction, divided by, start color #11accd, 40, end color #11accd, end fraction
start fraction, 3, divided by, 10, end fraction, times, start fraction, divided by, 4, end fraction, equals, start fraction, divided by, start color #11accd, 40, end color #11accd, end fraction
接下来,我们把分子和分母同乘以一个数:
start fraction, 7, divided by, 8, end fraction, times, start fraction, 5, divided by, 5, end fraction, equals, start fraction, 35, divided by, start color #11accd, 40, end color #11accd, end fraction
start fraction, 3, divided by, 10, end fraction, times, start fraction, 4, divided by, 4, end fraction, equals, start fraction, 12, divided by, start color #11accd, 40, end color #11accd, end fraction
这样异分母分数start fraction, 7, divided by, 8, end fractionstart fraction, 3, divided by, 10, end fraction化作了同分母分数.
start fraction, 7, divided by, 8, end fraction, equals, start fraction, 35, divided by, 40, end fraction
start fraction, 3, divided by, 10, end fraction, equals, start fraction, 12, divided by, 40, end fraction
注意: 新的分数与原来分数相同, 但是化作同分母分数后, 可以方便进行运算.
想要学习更多关于公分母的知识吗? 点击 视频.

练习

问题1
  • 当前
start fraction, 2, divided by, 5, end fractionstart fraction, 3, divided by, 10, end fraction通分( 且分子为整数).
哪个(些)数可以用作分母?
选择所有正确的答案:

想做更多此类练习,请点击 练习.

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