[問題]考古題Form14 sec6-Q16

[凱薩琳]

Each of 5 people paints at exactly the same rate. The 5 of them working together can paint a house in 36 hours. If only 3 of the people are working, how many hours will it take to paint the house than of all 5 were working?

(A)4
(B)8
(C)9
(D)12
(E)24

Ans: E

[scujean]

[解]這類屬於 距離/速率=時間 的題型 →總工作量/總速率=總時間
令原本五個人個別的速率為v,因為題目說五個人速率都相同
利用 總工作量/總速率=總時間→總工作量/[5*v]=36→總工作量=180*v
3個人的總工作時間=[180*v]/3v=60hr 60-36=24

[凱薩琳]

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