我想問以下呢幾題數......

1. Let x be the number of girls. Then number of girls wearing glasses is x/2.
Hence x/2 = 280*2/7
x/2=80
x=160

2. (8x+4)/2 -(3x-2)
=4x+2-3x+2
=x+4

3. [5(a+1)/2-4(a+1)]/3
={[5(a+1)-8(a+1)]/2}/3
=-3(a+1)/6
= (-a-1)/2

4. Let the height of the parallelogram be H cm and their base be B cm.
H*B = 5*B/2
H=5/2=2.5
The height of parallelogram is 2.5 cm

(1) Let number of girls wear glasses = x, let number of boys wear glasses = y
x = (2/7) y = (2/7) (280) = 80

Let total number of girls = z, x = 0.5z
z = 2x = 2 (80) = 160

(2) (8x+4 ) / (2-(3x-2))
= 4(2x+1) / (4-3x)

(3) 5(a+1) / (2-4(a+1)) / 3
= (5 (a+1) / (2 -4a -4) ) * (1/3)
= -10(a+1) / 3(2a+1)

(4) Let h = height of the triangle
area of parallelogram = HB
area of triangle = 0.5 * hB = 0.5 (5) B = 2.5 B

Because area of parallelogram = area of triangle
HB = 2.5B
Therefore height of the parallelogram = 2.5cm

2007-08-12 18:36:58 補充：
Revised Question (2) (8x 4 )/2 - (3x-2)= 4x 2 - 3x 2= x 4Revised Question (3)(5(a 1)/2- 4(a 1))/3= ((a 1) (5/2 - 4))/3= (a 1) (5 - 8) /6= -(a 1)/2