Chain Rule

Q 5: If 40 men can do a piece of work in 30 hours, then in how many hours will 12 men do it? A)120 hours B)100 hours C)80 hours D)90 hours Answer : Option B Explanation: Let the number of hours be x. 12 : 40 = 30 : x x=(40x30)/12=100 hours Q 6: A flagstaff 17.5 m high casts a shadow of length 40.25 m. The height of the building,which casts a shadow of length 28.75 m under similar conditions will be: A)11.8m B)10.5m C)15.8m D)12.5m Answer : Option D Explanation: Let the height of the building x meters less lengthy shadow.Less in the height(Direct Proportion) 40.25:28.75= 17.5:x =>40.25x=28.75x17.5 x=(28.75x17.5)/40.25=12.5m Q 7: A man completes 5/8 of a job in 10 days. At this rate, how many more days will it takes him to finish the job? A)5 B)3 C)6 D)5/2 Answer : Option C Explanation: Work done =5/8 Balance work =[1-(5/8)]=3/8 Let the required number of days be x. Then, 5/8:3/8=10:x =>(5/8)x=(3/8)x10 =>[(3/8)x10x(5/8)] =>x=6 Q 8: 100 books can be bind by 50 students in 4 hours. How many books will be bind by 150 students in 2 hours? A)150 B)100 C)160 D)120 Answer : Option A Explanation: Binding books is a work, so W2xS1xH1 = W1xS2xH2 W2x50x4 = 100x150x2 Solve W2 = 150 books

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