數學(Variations)@2

let C be the wxpense of running a summer camp and x be the number of students participated ,

then C=k_1 +k_2 x , where k_1 ,k_2 are real number ,

sub C=9650 and x=10 , we have 9650 = k_1+10k_2 --(1)

sub C=11600 and x=140 , we have 11600=k_1+140k_2--(2)

(2)-(1): 11600-9650 = (140-10)k_2
k_2=12 ,

sub k_2=12 into(1) ,we have k_1=9530 ,

so C=9530 + 12x//

ii) sub x =120 , C= 9530 +12(120)=$10970//



2009-03-24 21:46:19 補充：
Correct version :

sub C=9650 and x=110 , we have 9650 = k_1+110k_2 --(1)

sub C=11600 and x=140 , we have 11600=k_1+140k_2--(2)

(2)-(1): 11600-9650 = (140 -110) k_2

k_2=65

sub k_2 =65 into (1) , we have k_1 =2360

2009-03-24 21:46:57 補充：
so C=2360 + 65x//

ii) sub x =120 , C= 2360+65(120)=$10160

2009-03-24 21:48:39 補充：
sub k_2 =65 into (1) , we have k_1 =2500

so C=2500 + 65x//

ii) sub x =5120 , C= 2500+65(160)=$12900