Maths 一問 Quick

1) Let p be the price of a pig
c be the price of a cow

5p - 2c = 8000 -----------(1)
9p -4c = 10000 -----------(2)

(1)X2
10p - 4c = 16000 ----------(3)

(3)-(2)

p = 6000----(4)

Sub (4) into (1)
5(6000) - 2c = 8000
c = 11000



2) Let l be the length
w be the width

l = 2w --------(1)
2(l+w) = 48 -----------(2)

sub (1) into (2)

2(2w+w) = 48
6w =48
w = 8-----(3)
Sub (3) into 1

l = 2(8)
l = 16

so the dimension is 16 X 8

1) Assume the price of a pig is $X, and that of a cow is $Y.
5X-2Y=8000
and
9X-4Y=10000
X=(10000+4Y)/9

5X-2Y=8000
50000/9+4/9Y-2Y=8000
5/9(10000+4Y)-2Y=8000
50000+20Y-18Y=72000
2Y=22000
Y=11000

5X-2Y=8000
5X-2(11000)=8000
5X-22000=8000
5X=30000
X=6000

i.e.: A pig costs $6000 while a cow costs $11000

(I have to say that I'm not really sure about the 2nd Qs.)
2) Assume the Length of the rectangle is Lcm while the width of it is Wcm.
L=2W
and
2L+2W<48 (I can't type the symbol but there should a _ under the <)
2(2W)+2W<48
6W<48
W<8

L=2W
L<2(8)
L<16

i.e. The longest length is 16 while the longest width is 8.
Since: dimension=length x width
Thus: The longer the lengh and width is, the greater the dimension is. And the greatest dimension is to be: (16x8)cm square=128cm square
(Again, coz I can't type the symbol, plz change "since", "thus" and "cm square" ito the maths symbol.)