數學題........林極都林唔到.........急急急急急要係9月3日10:30比到答案我!!!!!

1) 設小明現在 x歲, 5年後是(x+5), 5年前是(x-5)
3(x-5)=(x+5)
3x-15=x+5
2x=20
x=10
所以小明現在10歲

2007-09-03 21:52:20 補充：
2) 設五角有x 個, 所以一元有3x 個3x 0.5x=213.5x=21x=6所以五角有6個

2007-09-03 21:53:57 補充：
3)15/(3 2)-4*2 10=15/5 -8 10=3 -8 10=5

2007-09-03 22:00:26 補充：
4)a*20%=1a*(0.2)=1a=1/0.2a=55)x-x/2=0.7你可唔可以寫 x-(x/2)=0.7x-(x/2)=0.7(2x-2)/2=0.7x=1.46)(1 25%)b=25(1 0.25)b=25(1.25)b=25b = 25/1.25 b=207)(70%-30%)y=1.6(40%)y=1.6(0.4)y=1.6y = 1.6/0.4 y= 4

2007-09-03 22:01:03 補充：
8)3b-5/7=0.521b-5=3.521b=8.5b = 8.5/21 b= 85/210 b=17/429)y/3-y/4=6/1y/3-y/4=64y-3y=72y = 72

2007-09-03 22:01:31 補充：
全部一定岩岩岩

1.設他先在是n歲
5年後=n+5
5年前的3倍=3(n-5)
n+5=3n-15
20=2n
n=10
2.設五角硬幣有x個
一元硬幣的數目=3x
3x+0.5x=21
X=6
3.
=15/5-8+10
= 5
4.aX20/100=1
a=100/20=5
5.x-x/2=0.7
10x-5x=7
x=7/5
6.1.25Xb=25
b=20
7.40y/100=1.6
y=4
8.42b-10=7
b=17/42
9.4y-3y=72
y=72
10.質數連乘式
質數=1,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,91,97
連乘式應該係乘曬佢掛

1. 設 x=現在年齡
x+5=3(x-5)
x+5=3x-15
20=2x
x=10

2. 設 x=1元數目, y=5角數目
i) x/y=3
x=3y
ii) 1*x+0.5*y=21
x= 21-0.5y
3y=21-0.5y
3.5y=21
y=6
3. 你條題打得唔多清楚, 到底 -4*2+10 係分開定連埋去(3+2)
等你搞掂我補番

4. a*20%=1
a=1/20%
a=5

5. x-x/2=0.7
(2x-x)
--------- = 0.7
2
x=1.4

6. (1+25%)b=25
b= 25 / (1+25%)
b= 25 / 1.25
b = 20

7. (70%-30%)y=1.6
(40%)y=1.6
y=1.6 / 40%
y=4

8. 3b-5/7=0.5
3b= 0.5 + 5/7
3b= 9.5 / 5
b=(9.5 / 5)/3
b= (9.5 / 5)*1/3
b=19/30

9. y/3-y/4=6/1
(4y-3y) / 12 = 6/1
y/12=6
y=6*12
y=72

唔知有冇計錯
不過多數岩

1.小明5年後的年齡是他5年前的3倍,問他先在是多少歲?
設現在是 x 歲
x+5 = 3(x-5)
x+5 = 3x-15
2x = 20
x = 10

2.一元和五角硬幣共直21元,若一元硬幣的數目是五角的3倍,問五角硬幣有多少個?
設五角硬幣有 x 個
一元硬幣的數目是 3x
(1)(3x) + (0.5)(x) = 21
3x + 0.5x = 21
3.5x = 21
x = 6

3.
15/(3+2)-4*2+10
= 15/5-4*2+10
= 3-4*2+10
= 3-8+10
= 5

4.
a*20%=1
a*(0.2)=1
a = 1/0.2 = 5

5.
x-x/2=0.7
2x - x = 1.4
x = 1.4

6.
(1+25%)b=25
(1+0.25)b=25
(1.25)b=25
b = 25/1.25 = 20

7.
(70%-30%)y=1.6
(40%)y=1.6
(0.4)y=1.6
y = 1.6/0.4 = 4

8.
3b-5/7=0.5
21b-5=3.5
21b=8.5
b = 8.5/21 = 85/210 = 17/42

9.
y/3-y/4=6/1
y/3-y/4=6
4y-3y=72
y = 72

2007-09-03 21:57:55 補充：
慢左, 不過上面第一位 三, 七題做錯左,請多多支持...

1. (x+5)=3(x-5)
x + 5 = 3x - 15
2x = 20
x = 10
2. 3x + .5x = 21
x = 6
3. 3 - 16 + 10 = -3
4. a = 1/20% = 1/.2 = 5
5. x/2 = 0.7
x = 1.4
6. b = 25/(1+25%)=25/1.25 = 20
7. (40%)y = 16
.4y = 16
y = 40
8. 21b - 5 = 7/2
21b = 17/2
b = 17/42
9. y/12 = 6/1
y = 72
If you typed it wrongly, such that y/12 = 1/6 then y = 2

2007-09-03 23:23:19 補充：
Sorry for the mistakes in Q3 and Q73. 3 - 8 10 = 57. (40%)y = 1.6 y = 4