急~F.2 maths Rate and Ratio~20點

你好～～～

以下都是本人的一些意見而已，如有錯誤請多多指教～～～

1. 1 / a : 1 : b = 3 : 2 ,1 /a : 1 / c =5 : 4

這條你應該打錯了些東西吧？

1) 1 / a : 1 / b = 3 : 2 , 1 / a : 1 / c = 5 : 4

(1 / a) / (1 / b) = 3 / 2

(1 / a) x b = 3 / 2

b / a = 3 / 2

a / b = 1 / (3 / 2)

a / b = 2 / 3

a : b = 2 : 3


1 / a : 1 / c = 5 : 4

(1 / a) / (1 / c) = 5 / 4

c / a = 5 / 4

a / c = 1 / (5 / 4)

a : c = 4 : 5


a : b : c

2 : 3
4 : 5

4 : 6 : 5

So，a : b : c = 4 : 6 : 5。


2) Harry is given 25 lucky draw coupons. he gets a prize on 5 of the coupons. what is the ratio of the number of coupons with prizes to that without prize?

The number of coupons with prizes: 25 / 5 = 5

The number of coupons without prizes: 25 - 5 = 20

So, the ratio is 5 : 20 = 1 : 4


希望可以幫到你～～～～～

2010-10-06 21:00:24 補充：
To Godfrey,

Ratio number of coupons with prize to number of coupon without prize

5:(25-[5]) = 5: 20

2010-10-06 21:14:01 補充：
Sorry，或許我那邊打錯了︰

應該是 The number of coupons with prizes: 5

2010-10-06 21:16:53 補充：
好的～～

2. harry is given 25 lucky draw coupons. he gets a prize on 5 of the coupons. what is the ratio of the number of ccoupons with prizes to that without prize?

問題現在是問你︰ratio of the number of ccoupons with prizes to that without prize?

亦即是說︰有獎 coupon 的數量與無獎 coupon 的比例。

2010-10-06 21:17:05 補充：
題目給了你︰有五張 coupons 得了獎（gets a prize on 5 of the coupons）

所以先得出 no of coupons with prizes 為 5。

2010-10-06 21:17:10 補充：
第二，要得出無獎的 coupon 的數量。

由於只有 5 張得了獎，所以無獎的有 (25 - 5) 張，無獎的 coupon 有 20張。

最後回答問題︰ratio of the number of ccoupons with prizes to that without prize?

當「頭的一個 to 後的一句」，就是「頭 : 後」

現在是有獎的 coupon 頭，無獎的後，所以為「5 : (25 - 5)」。

5 : (25 - 5)

5 : 20

1 : 4

所以答案為 1 : 4。

2010-10-07 20:16:50 補充：
Actually, I have already made a clarification of that:

「Sorry，或許我那邊打錯了︰

應該是 The number of coupons with prizes: 5 」

1. 1 / a : 1 : b = 3 : 2 ,1 /a : 1 / c =5 : 4

the ratio of 1/a to 1/b is 3 to 2, same as 3x5 to 2x5, 15 to 10
The ratio of 1/a to 1/c is 5 to 4, same as 5x3, 4 x3, 15 to 12

So the ratio of 1/a : 1/b : 1/c is 15 : 10: 12

If want a: b: c, that 1/15 :1/10: 1/12,
a:b:c: 60 /15:60/10,60/12
a:b:c  4:6:5

Answer: The ratio of 1/a : 1/b : 1/c is 15 : 10: 12
The ratio of a:b:c 4: 6: 5


2.harry is given 25 lucky draw coupons. he gets a prize on 5 of the coupons. what is the ratio of the number of ccoupons with prizes to that without prize?

Ratio number of coupons with prize to number of coupon without prize
 5:(25-20) = 5: 20

Answer:  1 to 4


2010-10-07 02:36:15 補充：
To 回答者：↗ Yogi™ ( 知識長 )

Sorry, it is my mistake. I mean to type :5 (25 - 5) = 5:20, otherwise I don't get 5:20

2010-10-07 02:44:48 補充：
To 回答者：↗ Yogi™ ( 知識長 )

Your final explanation is very clear, but I don’t understand your statement in the original solution.

Can you justify this statement: The number of coupons with prizes: 25 / 5 = 5