[F3 maths] 有關 percentages 一條難題

由 AP139 » 2011年2月24日 20:14:18 (p#2062896)

Copper and zinc are mixed together to form 2 alloys. Alloy X contains 22.5% copper by weight, and Alloy Y contains 65% zinc by weight. Alloy X and Alloy Y are melted to form Alloy Z which contains 30% copper by weight.

A) Find the amounts of Alloy X and Alloy Y needed to form 1000g of Alloy Z
B) If the prices of Alloy X and Alloy Y are $10 and $9 per gram respectively, and k gram of Alloy Z costs $470, find the value of k

諗左好耐都唔識...
tks

由無聊同志 » 2011年2月25日 10:24:37 (p#2063148)

(a) Let the weight of alloy X be x grams,
x(22.5%)+(1000-x)(100%-35%)=1000(30%)
x=400
∴Alloy X needed is 400g and Alloy Y is 600g.
(b) The cost of 1000g of alloy Z
=400($10)+600($9)
=$9400
k / 1000=470 / 9400
k=50

希望幫到你。 :smile:

由 AP139 » 2011年2月25日 19:59:01 (p#2063314)

無聊同志 :(a) Let the weight of alloy X be x grams,
x(22.5%)+(1000-x)(100%-35%)=1000(30%)
x=400
∴Alloy X needed is 400g and Alloy Y is 600g.
(b) The cost of 1000g of alloy Z
=400($10)+600($9)
=$9400
k / 1000=470 / 9400
k=50

希望幫到你。

但題目無寫明 alloy Z 就係 1000g, 點解答 a) 果題可以當左 alloy Z 就係 1000g?

由無聊同志 » 2011年2月25日 23:11:56 (p#2063507)

KR 3941．KG 4055 :Copper and zinc are mixed together to form 2 alloys. Alloy X contains 22.5% copper by weight, and Alloy Y contains 65% zinc by weight. Alloy X and Alloy Y are melted to form Alloy Z which contains 30% copper by weight.

A) Find the amounts of Alloy X and Alloy Y needed to form 1000g of Alloy Z
B) If the prices of Alloy X and Alloy Y are $10 and $9 per gram respectively, and k gram of Alloy Z costs $470, find the value of k

諗左好耐都唔識...
tks

KR 3941．KG 4055 :但題目無寫明 alloy Z 就係 1000g, 點解答 a) 果題可以當左 alloy Z 就係 1000g?

(a)就寫到明要溝成1000g的alloy Z，有問題嗎？