[計量] Magoosh數學請益

[gcat (夏天！)]

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?

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推 branda0423  :VA(velocityA=1.5/sec),VB假設=X, 先由(1.5+X)3=10算
→ branda0423  :出X,妳有VB就能算要多久啦
推 bear62479   :先算出A的效率 = 3/2 nails per s, 再假設b效率為y
→ bear62479   :最後AB合作效率帶進去解10N/3S就可以解出來了
推 kerotama    :B每秒5.5/3  故33/(5.5/3) = 18
推 Ghamu       :A:3n/2s A+B:10n/3s => A:9n/6s A+B:20n/6s
→ Ghamu       :=> B:11n/6s =>33n/18s  Ans:18sec
→ gcat        :原來是用效率的觀念~大感謝~