數學問題(3)

http://pic.fksite.com/1188010085.jpg
1) D
One ball=$x, 25ball= 25 x $x = $25x

2)A
現在,明=x歲
2 年後, 明= x + 2 歲
芳= 明2倍 = 2(x+2)
所以, 芳現在= 2(x+2)-2

3) B
積=相乘
所以=(2x)(9)-24

4) A

5)C
P=3x-4y
if x= 8, y=1
P= 3(8)-4(1)
= 24-4

6) C
x-3y=2-4x
if x=4, (4)-3y=2-4(4)
4-3y=-14
-3y=-14-4
y=-18/-3
y=6
= 20

7)a)2x
b)5m-5-2(2m+1)
= 5m-5-(4m+2)
= 5m-5-4m-2
= m-7

c)[2m+5)/2]-[(m-1)/4]
通份母,
= 2(2m+5)/4- (m-1)/4
= (4m+10-m+1)/4
= (3m+11)/4
d)6x[(2a+7)/3]+4x[(3a-5)/2]
= 約份母,
= 2(2a+7)+2(3a-5)
= 2(2a+7+3a-5)
= 2(5a+2)

8a)7x-2y,
if x=2,y=3
= 7(2)-2(3)
= 8

b)x/4+y/6
(2)/4+3(6)
= 1/2+1/2
= 1

c)(5x-2y)/4
(10-6)/4
= 1

9b)4x^2-2x+7-2x+3x^2+5x-2
= 7x^2+x+5 or x(7x+1)+5

d)2xy+3x-2y+4x-6y+5xy
= 7xy+7x-8y

10a) (4x+3y)/2xy
if x=3, y=5
[4(3)+3(5)]/2(3)(5)
= [27]/30
= 9/10

b) y/[x+1]+x/[y+1]
= 5/4+3/6
= 5(3)/12+3(2)/12
= [15+6]/12
= 21/12
=7/4

http://pic.fksite.com/1188010085.jpg
1) D
2) A
3) B
4) A
5) C
6) C
7a) 2X
7b) m-7

http://pic.fksite.com/1188010099.jpg
7c) 3m+9
--------
4

7d) 2(5a+2)
8a) 8
8b) 4
8c) 1
9b) 2
7x +x +5
9d) 7x-8y+7xy
10a)0.9
10b)7
---
4
10c) 13
11a)3
11b)2
11c)3

做住咁多先！