5N3.1 分數乘法 Fraction Multiplication

向學生展示一個數的分數倍數的意義,並發現 a/b × c/d = (ac)/(bd)。
http://www.geogebratube.org/student/m15555
 (Download GeoGebra file)

教育局「網上學與教支援」其他資源 

在下列各題中,拖拉紅點和藍點,顯示所求包數的米的重量。以勾選框顯示算式。

(a) 每包米重 2/3 公斤,4包米共重多少公斤? 2/3 × 4 應如何計算?
(b) 每包米重 4 公斤,2/3 包米重多少公斤? 4 × 2/3 應如何計算?
(c) 每包米重 4 公斤,1⅓ 包米共重多少公斤? 4 ×1⅓ 應如何計算?
(d) 每包米重 4/5 公斤,2/3 包米重多少公斤?4/5 × 2/3 應如何計算?
(e) 每包米重 1¾ 公斤,2⅔ 包米共重多少公斤?1¾ × 2⅔ 應如何計算?

Visualize the fraction multiples of a number and demonstrate
a/b × c/d = (ac)/(bd)
http://www.geogebratube.org/material/show/id/18168 
 (Download GeoGebra file)

In each of the following questions, drag the red and blue points
on the sliders to express the required weight by the shaded area
in the applet. Check the boxes to see how to calculate the weight.

(a) The weight of 1 bag of rice is 2/3 kg, what is the weight of 4 bags of rice? How to calculate 2/3 × 4?
(b) The weight of 1 bag of rice is 4 kg, what is the weight of
2/3 bag of rice? How to calculate 4 × 2/3 ?
(c) The weight of 1 bag of rice is 4 kg, what is the weight of
1⅓ bags of rice? How to calculate 4 ×1⅓ ?
(d) The weight of 1 bag of rice is 4/5 kg, what is the weight of 
2/3 bags of rice? How to calculate 4/5 × 2/3 ?
(e) The weight of 1 bag of rice is 1¾ kg, what is the weight of 
2⅔ bags of rice? How to calculate 1¾ × 2⅔ ?