F.1數學,,,,,,,,(ratio)

1. Given that (a+2) : (a+5) : b=3 : 4 : 7.Find the values of a and b.
(a+2) / (a+5) = 3/4
4(a+2) = 3(a+5)
4a + 8 = 3a + 15
a = 7
(a+5) : b= 12 : b= 4 : 7
12 / b= 4 / 7
b = 21
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2. 1/2 : 7 =5 : a =2b : 56
(1/2) / 7 = 5 / a
1/14 = 5 / a
a = 70
5 : 70 =2b : 56
5 / 70 =2b / 56
b = 2
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3. Given that x + y = 39 and x : y = 4 : 9
(a) For expression x : y = 4 : 9,express x in terms of y
x / y = 4 / 9
x = 4y / 9

(b) Hence, find the values of x and y
4y / 9 + y = 39
13y / 9 = 39
y = 27

2008-02-09 15:03:55 補充：
3b)x + 27 = 39 x = 12

2008-02-16 07:25:03 補充：
要補補佢嘛 ??

1. Given that (a+2) : (a+5) : b=3 : 4 : 7.Find the values of a and b.
(a+2) : (a+5) = 3 : 4
4(a+2) = 3(a+5)
4a+8 = 3a+15
a = 7

(a+5) : b = 4 : 7
12 / b = 4 / 7
b = 21


2. 1/2 : 7 =5 : a =2b : 56
1/2 : 7 =5 : a
0.5 / 7 =5 / a
a = 70

5 : a =2b : 56
5 / 70 = 2b / 56
2b = 4
b = 2


3. Given that x + y = 39 and x : y = 4 : 9
a) For expression x : y = 4 : 9,express x in terms of y
x : y = 4 : 9
x / y = 4 / 9
x = 4y / 9

b) Hence, find the values of x and y.
(4y / 9) + y = 39
4y / 9 = 39 - y
4y = 351 - 9y
13y = 351
y = 27

x + y = 39
x + 27 = 39
x = 12

1)
(a+2) : (a+5)=3:4
4a+8=3a+15
a=7

(a+5) : b=4 : 7
12/b=4/7
b=21

2)
1/2 : 7 =5 : a
1/14=5/a
a=70

5 : a =2b : 56
1 :14 =b : 28
b=2


3a)
x : y = 4 : 9
x/y=4/9
x=4y/9

b)x + y = 39
4y/9+y=39
13y/9=39
y/9=3
y=21

x=4y/9
x=9

The values of x and y is 9 and 21.

2008-02-09 15:07:07 補充：
3b)x + y = 39 4y/9+y=3913y/9=39y/9=3y=27x=4y/9x=12The values of x and y is 27 and 12.