--超趕 , 30 marks -- 各位知識朋友 , 入黎幫我手 ar !!! ( 數學F.1 ) (56)

Like calculationg LCM.
(a) 兩個ratio都有 "c", (c=5, c=2), 所以將兩個c 倍大,變成同一個數值, 先比較到.
5 同 2, 大家都可以倍大到 10
c 倍大, 咁同佢比較 o個個 "a" 同"b" 當然都要倍大啦.
所以, a:c=8:5, 倍大成為 a:c=16:10 (a同c 都 乘左二,先令 c 倍大到去 10)
而b:c=3:2, 倍大成為 b:c=15:10 (b同c 都乘左五,先令到c 倍大到去10)

而家兩個ratio o既 c 都係10, 所以就可以將a 同 b 同 c一齊比較
a:b:c = 16:15:10

(b) 兩個raio都有"b" (b=7, b=14)
7 同 14, 只要將"7" 倍大到去 "14", 就已經比較到, 個14 唔駛倍大架喇.
所以a:b=3:7, 倍大成為 a:b=6:14 (a同b 都 乘左二, 令到b 倍大到去14)

而家兩個ratio o既b都係 14, 可以將a同b同c一齊比較
a:b:c=6:14:15

ratio o既重點就係要 幾樣野都o係一個公平o既情況下先比較到.
就好似你有6支筆, 人地有3把間尺,比較"多少".
個單位唔同,點比較? 都唔公平.
除非人地將三把間尺換成9支筆 (假設佢一把間尺o既價錢買到3支同你一模一樣o既筆,三把間尺就換到9支筆)
咁先比較到多少, 咁先公平.
希望你明白ratio點計啦

(a) a:c=8.5,b:c=3.2
將相同的c同化(即找LCM)
a:c=16:10,b:c=15:10
再對位
a : c
b :c
--------------
16:15:10
所以a:b:c=16:15:10
(b) a:b=3:7,b:c=14:15
又係找b的LCM
a:b=6:14,b:c=14:15
對位
a :b
b :c
-----------------
6:14:15

交叉相乘好就咁講好難，要用箭頭。希望你睇得明啦!!

2008-02-23 23:20:52 補充：
點解我f.2先教.....

( a ) a : c = 8 : 5 , b : c = 3 : 2
a : c = 8x2 : 5x2 ,
16 : 10
b : c = 3x5 : 2x5
15 : 10
(a) a:b:c=16:15:10

( b ) a : b = 3 :7 , b : c = 14 : 15
3x2 :7x2
6:14
(b)a:b:c=6:14:15

其實ok易...好似第一題咁.
把兩個c都變做一樣(公倍數)
其他都係咁...希望你明啦~

(a) a : c = 8 : 5 , b : c = 3 : 2

a:c=8x2:5x2-->16:10

c:b=2x5:3x5-->10:15

so c:a:b=16:10:15 -->a:b:c=10:15:16
---------------------------------------------------------------------------------
(b)a : b = 3 :7 , b : c = 14 : 15

a : b = 3 :7 --> 3x2:7x2-->6:14

b : c = 14 : 15-->14x1:15x1-->14:15

so a:b:c=6:14:15

a:b:c=24:10 :15

steps are as follows:

a : c1 = 8 : 5
> c2 : b = 3 : 2
------------------------------------------------------------------------
= a x c2 :c1x c2 :b x c1 24 : 15 : 10

to find a , times a by c2 to find the COMMON FACTOR! that is 24
to find b , times b by c1 to find the COMMON FACTOR! that is 10
to find c just time both c together to find the COMMON FACTOR ,and that is 15

其實好簡單,
e.g in this case,

將a:c個a 乘c:b個 c,即係8x3 = 24

而兩個c又相乘,就會得出5x3 = 15

由於a:c中,a同c都乘同一個數,佢地之間既ratio係冇變的 (都係8:5)

同樣地, c:b中的b同a:c中的c相乘,就會得出2x5 = 10,

而c :b中的c就同上面的c相乘,即係3x5 = 15,

大家乘5,ratio冇變,,最後得到的答案就係24比15比10,

如果分返開佢地,個ratio係同一開始比的係一樣的,所以答案就冇錯喇





B亦都係同樣做,,而答案就係a x b2( 3x14) : b1 x b (7x14) : c x b1 (15x7)
> = 42 : 98 : 105

次次都係咁做架渣,冇特別的!,掌握到就冇難度了!

2008-02-23 22:42:30 補充：
第一條c同b掉轉左..sorry..應該係8x2: 3x5: 2x516:15:10

2008-02-23 22:44:55 補充：
第2條可以再約簡,全部除7 = 6:14:15唔好意思

(a) since c is present in the two ratio, we can make c the same number

a:c=8:5 a:c=16:10 (all times 2)

b:c=3:2 b:c=15:10 (all times 5)

a:b:c = 16:15:10

(b) a:b=3:7 a:b=6:14 (all times 2)

b:c=14:15


a:b:c=6:14:15

(a) a:c = 8:5 , b:c = 3:2
經過交叉相乘後........
a:c:b = 16:10:15 (final answer)

(b) a:b = 3:7 , b:c = 14:15
經過交叉相乘後........
a:b:c = 6 : 14 :15 (final answer)

I hope you know what is 交叉相乘 la.....^^

(a)a:c=8:5
b:c= 3:2
—————
a:b:c=24:15:10 (將3乘8,3乘5,2乘5)
(b)果題用同一個方法做就ok!

2008-02-23 22:27:39 補充：
樓上果位人兄應該做得不對吧!

a) a : c = 8 : 5 = 16 : 10
b : c = 3 : 2 = 15 : 10
a : b : c = 16:15:10

b) a : b = 3 : 7 = 6 : 14
b : c = 14 : 15
a : b : c = 6:14:15

嘩..
都唔係好明呀...
你中5呀.......