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作者: r9r9r9r9    時間: 2016-8-11 01:00 AM     標題: 數學廢

1.Mrs chan used $60 to buy some mangoes. If the price of each mango is increased by $1 she will buy 2 mangoes less with $60 . Find the original price of each mango
2.mr chan distributes 120 cups evenly into a certain number of boxes . If 3 fewer boxes are used , each boyx has to contain 2 more cups .how many boxes are there originally?
3. The area of an isosceles right -angled triangle is x/2 cm^2 . If the base increased by 2 cm and height is decrease d by 1 cm, the area of new triangle is 14 cm^2. Find x
求好心人比條式我
我諗左好耐




作者: HermionePct    時間: 2016-8-11 10:32 AM     標題: Question 1 solution

Let x be the original price of the mangoes.
Let y be the original amount of mangoes.

xy=60---(i)
(x+1)(y-2)=60---(ii)

In (i),
xy=60
y=60/x---(iii)

Sub (iii) into (ii)
(x+1)(60/x-2)=60
x=5 or -6(rejected)

Therefore, the original price of each mango is $5.
作者: HermionePct    時間: 2016-8-11 10:38 AM     標題: Question 2 solution

Let x be the original number of boxes used.
Let y be the original no of cups one box contains.

xy=120---(i)
(x-3)(y+2)=120---(ii)

In (i),
xy=120
y=120/x---(iii)

Sub (iii) into (ii)
(x-3)(120/x+2)=120
x=15 or -12

Therefore, the original no of boxes used is 15.
作者: r9r9r9r9    時間: 2016-8-11 11:53 AM

要用more about quadratic equations




作者: nanaliu    時間: 2016-8-11 07:30 PM

Push
作者: nanaliu    時間: 2016-8-12 01:45 PM

推多一次
作者: nanaliu    時間: 2016-8-12 07:14 PM

點解無人答
作者: nanaliu    時間: 2016-8-13 04:37 PM

再推多一次
作者: ericleung0413    時間: 2016-8-13 06:41 PM     標題: Question 3 solution

let a cm be the base of the original triangle'
(a+2)(a-1)/2=14
a^2+a-2=28
a^2+a-30=0
a=5 or -6(rejected)

so x = a^2
        =25
作者: nanaliu    時間: 2016-8-14 03:19 PM

仲有第1,2題未答到,再換推一推
作者: him5doublestars    時間: 2016-8-14 11:09 PM

(x-3)(120/x+2)=120
x=15 or -12




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