[計量] Magoosh數學請益

看板GRE作者 (夏天！)時間12年前 (2013/10/11 15:34), 編輯推噓4(4推 0噓 4→)
留言8則, 5人參與, 最新討論串1/1
想問一下Magoosh數學裡面的一題， Machine A can make 3 nails in 2 seconds. Working together, machines A and B can make 10 nails in 3 seconds. How many seconds does it take machine B to make 33 nails? 答案是18，但還是不懂怎麼解的? -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 219.87.185.205
推
10/11 15:47, , 1F
VA(velocityA=1.5/sec),VB假設=X, 先由(1.5+X)3=10算
10/11 15:47, 1F
→
10/11 15:47, , 2F
出X,妳有VB就能算要多久啦
10/11 15:47, 2F
推
10/11 15:48, , 3F
先算出A的效率 = 3/2 nails per s, 再假設b效率為y
10/11 15:48, 3F
→
10/11 15:48, , 4F
最後AB合作效率帶進去解10N/3S就可以解出來了
10/11 15:48, 4F
推
10/11 15:53, , 5F
B每秒5.5/3 故33/(5.5/3) = 18
10/11 15:53, 5F
推
10/11 16:11, , 6F
A:3n/2s A+B:10n/3s => A:9n/6s A+B:20n/6s
10/11 16:11, 6F
→
10/11 16:12, , 7F
=> B:11n/6s =>33n/18s Ans:18sec
10/11 16:12, 7F
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10/13 20:32, , 8F
原來是用效率的觀念~大感謝~
10/13 20:32, 8F
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