人教版七年级数学第九章实际问题与一元一次不等式答案.doc

人教版七年级数学第九章实际问题与一元一次不等式答案一、选择题 1.( 1703 )A.;2.( 1810 )A.;3.( 1754 )D.;4.( 3134 )D; 5.( 2327 )D.; 解析: 设爸爸的的体重为 x kg, 小芳的体重为 y kg, 则妈妈的体重为 2y kg. 根据题意可知 x +3 y= 150 x >3 y 解之得 y <25 .6.( 3036 )C.; 二、填空题 7.( 3562 ) 360 ;8.( 1776 )1<a<7;9.( 1794 ) 60<x< 80; 10.( 3081 ) 200 , 150 ; 11.( 3140 ) 63000 ; 12.( 3165 ) ; 13.( 4414 ) 13; 14.( 4417 ) 450 ; 15.( 7399 )6<x< 12 提示:由三边关系可知: 4-3<x-5< 4+3 ; 三、解答题 16.( 3206 ) 解:方案(一) 获利: 140 × 4500 = 630000 (元) 方案(二) 获利: 140 -6× 15= 50(吨)6× 15× 7500+50 × 1000 = 725000 (元) 方案(三) 获利:设 x 天精加工, y 天粗加工 15 6 16 140 x y x y ? ???? ??,解之得 105 xy ?????, 10×6× 9500+5 × 16× 4500 = 810000 (元) ∵ 810000 》∴方案三获利最多。 17.( 6993 ) 解: (1) 设最多可购买乙树苗 x 棵,则购买甲树苗( 600 x?)棵················· 1分 60(600 ) 80 44000 x x ? ?≤·············································································· 3分 400 x ≤. 答:最多可购买乙树苗 400 棵. ········································································· 5分(2) 设购买树苗的费用为 y则 60(600 ) 80 y x x ? ?? 20 36000 y x ? ?···························································································· 6分根据题意 (600 ) 600 x x ? ? ?≥ 150 x?∴当 150 x?时, y 取最小值. ··········································································· 8分 min 20 150 36000 y ? ?? 39000 ?. 答:当购买乙树苗 150 棵时费用最低,最低费用为 39000 元. ·································· 9分 18.( 7071 ) 解: (1) 设生产 A 型桌