暑期作業~數學~唔識呀*help~me~*15點

1)
1/f = 1/u + 1/v
1/f = 1/4 + 1/2
1/f = 1/4 + 2/4 = 3/4
f = 4/3

2)
設最多可放書 x 本
2 + 3x < 72
3x < 70
x < 70/3
x < 23.3333

要整數, 即係 最多可放書 23 本

3)
(2m+1)/3 = 2 - m
2m+1 = 3(2 - m)
2m+1 = 6 - 3m
5m + 1 = 6
5m = 5
m = 1

4)
x/3 - x/2 + 1 = 0
x/3 - x/2 = -1
6(x/3 - x/2) = -6
2x - 3x = -6
-x = -6
x = 6

5)
設甲、乙、丙三人分 x, y, z kg 的米
x = (1/3)y ----------- (1)
y = 5z ---------- (2)

代 (2) 入 (1), x = (1/3)(5z) = (5/3)z

x + y + z = 69
(5/3)z + 5z + z = 69
5z + 15z + 3z = 207
23z = 207
z = 9
y = 5z = 45
x = (5/3)z = 15

甲、乙、丙三人分 15, 45, 9 kg 的米

6)
ai)
每盒CD-R 的售價
= 128 + (0.22)(100)
= 150

ii)
每箱CD-R 的售價
= (150)(100)
= 15000

每箱成本
= (128)(100)
= 12800

每箱的盈利百分率
= (15000 - 12800)/12800 * 100%
= 17.1875%

1.you mean f分之1=u, u分之1 ar ????

1/f=u , 1/u+1/v

f=1/u

f=1/(1/4)+1/2
so , f=4.5

2.
72-2
=70
70/3
=23.33333
because book cut cut into 0.3 , so take it 23

so , it can put 23 books

3.

(2m+1)/3=2-m
2m+1=6-3m
5m=5
m=1

4.
x/3-(x+1)/2=0
(2x-3x-3)/6=0
2x-3x-3=0
-x=3
x=-3

(一)
1/f=1/u+1/v
1/f=1/4+1/2
1/f=3/4
f=4/3
f=1又3分1
(二)膠箱最多可放書:
(72-2)/3
=23本...1kg
膠箱最多可放書23本
(3)
3分之1(2m+1)=2-m
2m+1=3(2-m)
2m+1=6-3m
2m+3m=6-1
5m=5
m=1
(4)
3分之x-2分之x+1=0
(6分之2x)-(6分之3x)+(6分之6)=0
2x-3x+6=0*6
-1x=0-6
-1x= -6
x=6

1/Substitute u = 4 and v = 2 into the formula 1/f = 1/u + 1/v,
1/f = 1/4 + 1/2
1/f = 3/4
1 = (3/4)f
f = 4/3

2.72 - 2 = 70
So, the books cannot be heavier than 70 kg
70/3 = 23 ... 1
So, the box can hold 23 books.

3.1/3 x (2m + 1) = 2 - m
2m + 1 = 6 - 3m
5m = 5
m = 1

4.x/3 - x/2 + 1 = 0
2x + 3x + 6 = 0
5x = -6
x = -6/5

5.Let y kg be the amount of rice C get.
Then B get 5y kg.
Then A get 5y/3 kg.
Hence, we can set up an equation:
5y/3 + 5y + y = 69 (=total amount of rice)
5y + 15y + 3y = 207
23y = 207
y = 9

i.e. C gets 5 kg.
So, B gets 5 x 9 = 45 kg and A get 45/3 = 15 kg.

6ai)Price of each CD-R = $128 / 100 + 0.22 = $1.5
Price of each packet of CD-R = $1.5 x 100 = $150

ii) Original price for a box of CD-R = $128 x 100 = $12800
New price = $150 x 100 = $15000

Profit %
= ($15000 - $12800)/$12800 x 100%
= 17.1875%
(= 17.2 % (corr. to 3 sig. fig.))

b) Price for each CD-R under the new scheme = $75 / 50 = 1.5
The price is the same as that in (a)(ii), hence the profit percentage is also the same, which is 17.1875%.