Seema works at a rate such that she can finish a work in 28 h, but she works at this rate for 7 h only . After that , she works at a rate such that she can finish the whole work in16 h. If Seema is to finish this work at a stretch, how many hours(total) will she take to finish this work?

Explanation

Given: Seema works at a rate such that she can finish the work in 28 h Concept used: Total work = Efficiency of the worker × time taken by him Calculation: Let the efficiency of Seema be x units/h Now, Total work = 28 × x ⇒ 28x In 7 hours she will complete 7 × x = 7x units Remaining work = 28x - 7x = 21x If Seema completes the whole work in 16 hours then her efficiency = 28x/16 ⇒ 7x/4 So, The remaining work is completed = 21x/(7x/4) ⇒ 12 hours Total time = 7 + 12 ⇒ 19 hours ∴ She will take 19 hours to finish this work.