F.3 Maths 5點

4. (x-3/5)-(2+5x/3)≦9
3(x-3)/15 - 5(2+5x)/15 ≦9
(3x-9-10-25x)/15 ≦9
-22x - 19 ≦135
-22x ≦154
x ≧ 154/-22
x ≧ -7

6.Let x be the largest one of the three consecutive odd integer.
(x-4) + (x-2) + x ≧ 100
3x - 6 ≧ 100
3x ≧ 106
x ≧ 106/3
x ≧ 35.33
Therefore, the least possible value of the largest odd integer
is 37 (36是雙數!)

7.Let x and y be the prices of apple and orange respectively.
5x + 9y > 50
In order to obtain the minimum price of orange, the price of apple should be maximal, which is $3.5, in the calculation
5(3.5) + 9y > 50
9y > 32.5
y > 3.6
Therefore, the minimum price of orange is $3.7
(取3.6+0.1係因為correct to the nearest $0.1,唔會3.62, 3.63...)

5.3/4(x+1)+2/5(4-x)≧2
3*5(x+1)/20 + 2*4(4-x)/20 ≧2
15x + 15 + 32 - 8x ≧40
7x ≧40 - 47
x ≧-7/7
x ≧ -1

我唔知(x+1)同(4-x)係擺係分子OR分母
我當係擺係分子黎計
如果唔係既話市補充:)


2011-10-16 00:12:21 補充：
市=請