F.2 (2條)急!!英文數 15點!!! 感激不盡

2009-09-29 12:14 am

2. Suppose that 3a=5b=2c and a is greater than b by 14.

(a) Find the ratio a : b : c

(b) Find the values of a,b and c.

3. Suppose that a, b and c (where a< b < c ) are 3 consecutive even numbers. If a : c = 5 : 6, find the numbers a, b and c.

4.Gary stands in front of a lamppost at B . He puts a mirror M on the ground and sees the reflection of the top of the lamppost C as shown inthe figure. It is known that ∠AMB = ∠CKD.
ab =1.5 m, CD = 6m and BD =15m.

(a) Which triangle is similar to △ABM?
(b) fIND THE RATIO BM : DM.
(c) Hence find the length of DM.

更新1:

係3條,Sorry / \

更新2:

有式, ＋５點!!!

更新3:

你可以吾答第４條- ]

更新4:

我改一改第４條, 4.The ratio of the number of marbles owned by Susan to the number of marbles owned by Teresa is 5 : 2. Susan has n marbles. If Susan gives 18 of her own marbles to Teresa, both of them will have the same number of marbles.Find n.

回答 (3)

[匿名]

2009-09-29 12:48 am

✔ 最佳答案

2.(a)
3a = 5b
a/b = 5/3
a : b = 5 : 3

3a = 2c
a/c = 2/3
a : c = 2 : 3

a:b = 5 x 2 : 3 x 2 = 10 : 6
a:c = 2 x 5 : 3 x 5 = 10 : 15

a : b : c = 10 : 6 : 15

2.(b)
a = b+14
3a = 5b
3b + 42 = 5b
2b = 42
b = 21

a = 21 + 14
a = 35

3a = 2c
2c = 105
c = 52.5

3.

c = a + 4

a:c=5:6
a/c=5/6
a/(a+4)=5/6
6a=5a+20
a=20

b=20+2=22

c=20+4=24

4. 未有圖

2009-09-28 17:28:29 補充：
4.
suppose susan has m marbles.

n : m = 5 : 2
n / m = 5 / 2
n = 2.5 m ---1

n - 18 = m + 18
n = m + 36 ---2

Sub 2 into 1
m + 36 = 2.5m
1.5m = 36
m = 24 ---3

sub 3 into 2
n = 24 + 36
n = 60

2009-09-28 17:29:06 補充：
係suppose teresa has m marbles.

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HongBert

2009-09-29 12:50 am

2.
3a=5b=2c , and set a=b+14

3(b+14)=5b
3b+42=5b
42=5b-3b
42=2b
b=42/2
b=21

because a=b+14
so a=21+14
a=35

because 5b=2c
so 5X21=2c
105=2c
c=105/2
c=52.5

Ans:

(a) ratio of a:b:c is
35 : 21 : 52.5
70 : 42 : 105
divided by 7,
10 : 6 : 15

(b)
a=35
b=21
c=52.5

3.
set a+2=b , b+2=c
a:c is 5:6

because a+2=b
a=b-2

a/c = 5/6
(b-2) / (b+2) = 5 / 6
5(b+2) = 6(b-2)
5b+10 = 6b-12
10=6b-12-5b
10=b-12
b=10+12
b=22

because a+2=b
a+2=22
a=22-2
a=20

because b+2=c
22+2=c
c=24

Ans:
a=20
b=22
c=24

4.
can't see your figure as the question stated wu.....
so don't understand the question la.
can u provide clearly so that I can answer it?

參考: me

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用戶9112

2009-09-29 12:39 am

Where is the figure for question 4?

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