中二一元一次不等式..要完整..

1. 設$2有X個, $5有(20 - X)個
2x + 5(20 - x) >= 85
2x + 100 - 5x >= 85
-3x >= -15
x <= 5

他最多有5個$2.

2. 設黃小姐x kg, 何先生1.5x kg
x + 1.5x <= 124
2.5x <= 124
x <= 49.6

所以何先生的體重最大是 74.4kg.

3. 設闊度為x cm, 長度則為(3x - 8) cm
2[x + (3x - 8)] >= 24
2(x + 3x - 8) >= 24
2(4x - 8) >= 24
8x - 16 >= 24
8x >= 40
x >= 5

所以長方形面積最小為 5(3*5 - 8) = 35cm^2.

4. 你打漏左野....

5. (x + 1)/2 - [2(x - 1)]/3 <= 1/6
3(x + 1) - 2[2(x - 1)] <= 1
3x + 3 - 2(2x - 2) <= 1
3x + 3 - 4x + 4 <= 1
-x <= -6
x >= 6

6. -0.8(x - 1) + 0.6(2x + 1) > x
-0.8x + 0.8 + 1.2x + 0.6 > x
-0.6x + 1.4 > 0
0.6x < 1.4
x < 7/3

7. (3x + 4)/5 - (7x - 3)/2 > (x - 16)/4
4(3x + 4) - 10(7x - 3) > 5(x - 16)
12x + 16 - 70x + 30 > 5x - 80
-63x > -126
x < 2

1. x + y = 20 2x + 5y >= 85

2x + 5(20-x) >= 85

100 - 3x >= 85

x <= 3

so he has 3 nos. of $2 coin max.

2. w + h <= 124 h = 1.5w

5/3 h <=124

h<= 74.4kg

so max. h = 74.4

3. L = 3W - 8 2(L+W) >=24

8W - 16 >=24

W >= 5

so the min. W = 5 and L = 7, min. area = 35cm^2

4. What is (1-/3)??????????

5. (x+1)/2 - [2(x-1)]/3 <= 1/6

3x + 3 -4x +4 <=1

x>=6

6. -0.8(x-1) + 0.6(2x+1)>x

-8x + 8 + 12x + 6 > 10

x > -1

7. (3x+4)/5 - (7x-3)/2 > (x-16)/4

4(3x+4) - 10(7x -3) > 5(x-16)

12x + 16 - 70x + 30 > 5x - 80

126 > 63x

x < 2