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20. Donna buys some 2 dolars stamps and some 5 dollars stamp,if she spends 54 dollars altogether and gets 15 stamps,how many 2 dollars does she buy?19.In a class of 45 students, the number of girls is more than the number of boy by11.(1)how many girls are there in the class?(2)how many boys are there in the... 顯示更多 20. Donna buys some 2 dolars stamps and some 5 dollars stamp,if she spends 54 dollars altogether and gets 15 stamps,how many 2 dollars does she buy? 19.In a class of 45 students, the number of girls is more than the number of boy by11. (1)how many girls are there in the class? (2)how many boys are there in the class? 16. 3/4x-2(x-24)=3

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不好意思.妳還記得我答過妳這條問題嗎?? 謝謝妳選了我為最佳答案, 以下那一題, 我答錯了. 不好意思喔~~~~~ 12. x/4-x+1/8=2 (x/4-x+1/8) * 8 = 2 * 8 2x - 8x + 8 = 16 -6x = 16 - 8 -6x = 8 x = - 4/3 正確應是 : 12. x/4-x+1/8=2 (x/4-x+1/8) * 8 = 2 * 8 2x - 8x + 1 = 16 -6x = 16 - 1 -6x = 15 x = - 2.5 2006-10-19 20:45:36 補充： 20. LET X AND Y BE THE 2 DOLLARS STAMPS AND 5 DOLLARS STAMPS WHICH DONNA BYS RESPECTIVELY.X + Y = 15---------(A)2X + 5Y = 54------------(B)FROM (A), X + Y = 15 X = 15 - Y ----------- (C) 2006-10-19 20:45:55 補充： INSERT (C) INTO (B),2X + 5Y = 542* (15-Y) + 5Y = 5430 - 2Y + 5Y = 543Y = 54 - 303Y = 24Y = 8FROM (C), X = 15 - Y X = 15 - 8 X = 7.THEREFORE, DONNA BUYS 7 - 2 DOLLARS STAMPS. 2006-10-19 20:50:08 補充： 19) LET X AND Y BE THE NUMBERS OF GIRLS AND BOYS RESPECTIVELY.X + Y = 45 --- (A)Y = X - 11------(B)INSERT (B) INTO (A),X + Y = 45X + (X - 11) = 452X - 11 = 452X = 45 + 112X = 56X = 28THEREFORE, THERE ARE 28 GIRLS IN THE CLASS. 2006-10-19 20:51:59 補充： FROM (B), Y = X - 11 AND WE KNOW X = 28, Y = 28 - 11 Y = 17THEREFORE, THERE ARE 11 BOYS IN THE CLASS. 2006-10-19 21:05:27 補充： 16.) 3/4x-2(x-24)=3 3/4x - 2x + 48 = 3 3/4x - 2x = 3 - 48 3/4x - 2x = -45 -1.25x = - 45 x = 36

其他解答:

20. Donna buys some 2 dolars stamps and some 5 dollars stamp,if she spends 54 dollars altogether and gets 15 stamps,how many 2 dollars does she buy? let x be the number of $2 stamp,then the number of $5 stamp is 15-x 2x+5(15-x)=54 2x+75-5x=54 75-3x=54 3x=21 x=7 so she buys 7 $2 stamps 19.In a class of 45 students, the number of girls is more than the number of boy by11. (1)how many girls are there in the class? let x be the number of girls in the class then the number of boys is x-11 x+(x-11)=45 2x-11=45 2x=56 x=28 so there are 28 girls in the class. (2)how many boys are there in the class? the number of boys =45-28 =17 so there are 17 boys in the class. 16. 3/4x-2(x-24)=3 3/4x-2x+48=3 45=5/4 x x=36|||||20.7 2dolars stamps 19.(1)34 (2)11 16. Do not know|||||let she buys x 2 dollars stamps ,y 5 dollars stamp then x+y=15 2x+5y=54 from (1) y=15-x 2x+5(15-x)=54 -3x=-21 x=7 she buy 7 "2 dolars stamps " 19 let there are x boys then there are x+11 girls x+x+11=45 x=17 so there are 17 boys ,28 girls 3/4x-2(x-24)=3 3x-8x+192=12 -5x=-180 x=36|||||20. ans is 7 19. 28girls 17boys