1.

Rashid can complete a job by himself in 15 days while kausik can do the same work alone in 21 days. If they work together how many days will it take them to complete the work?1. \(8\frac{3}{4}\)2. \(9\frac{1}{4}\)3. \(8\frac{1}{4}\)4. \(9\frac{3}{4}\)

Answer» Correct Answer - Option 1 : \(8\frac{3}{4}\)

Given: work together how many days will it take them to complete the work?

R can do work = 15 days

K can do work = 21 days

Concept used:

Total work = LCM

Formula used:

Efficiency = Work/Time

Calculations:

Total work = LCM of 15 and 21 = 105

Person

Time

Total work

Efficiency

R

15 days

105

105/15 = 7

K

21 days

105

105/21 = 5

R + K

= 105/12

= 8(3/4) days

105

12

 

Then efficiency of R+K = 7 + 5 = 12

The efficiency of R ∶ K  = 7 ∶ 5

∴ Working together they completed the work in 8(3/4) days.



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