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Maths question??

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1.)480,240,120,60,30 The common ratio: The 6th term: 4,12,36,108,324 The common ratio: The 6th term: 3.)Man is 7 years older than Shan ,and their total age is at least 51.Find their least possible ages. 更新: http://hk.knowledge.yahoo.com/question/?qid=7006111204210

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1.)480,240,120,60,30 The common ratio: 30 The 6th term:15 4,12,36,108,324 The common ratio:4 The 6th term:972 3.)Man is 7 years older than Shan ,and their total age is at least 51.Find their least possible ages. let y be the age of Shan, y+7 be the age of Man y+y+7=51 2y=44 y=22 Man is 29 years old. Shan is 22years old.

其他解答:

1.) 480,240,120,60,30 The common ratio:1/2 lets T(1)=480,T(2)=240,T(3)=120,... T(2)/T(1)=1/2 T(3)/T(2)=1/2 ... so, ratio=1/2 The 6th term:15 T(n)=aR^(n-1) if a=480,R=1/2 T(6)=(480)(1/2)^(6-1) T(6)=15 4,12,36,108,324 The common ratio:3 lets T(1)=4,T(2)=12,T(3)=36,... T(2)/T(1)=3 T(3)/T(2)=3 ... so, ratio=3 The 6th term:972 T(n)=aR^(n-1) if a=4,R=3 T(6)=(4)(3)^(6-1) T(6)=972 3.)Man is 7 years older than Shan ,and their total age is at least 51.Find their least possible ages. T(n)=a+(n-1)d if d=7, T(n)+T(n+1)>=51, Man's ages -- T(n+1)=a+(n)7.....(1) Shan's ages - T(n)=a+(n-1)7......(2) (1)+(2), 2a+14n-7>=51 2(a+7n)>=58 a+7n>=29 if a+7n=29 T(n+1)=a+7n=29 T(n)=a+7n-7=22 so, Man's ages is 27, Shan's ages is 22