AFCAT Model Paper 4

GIVEN: Saral, Ravi and Karan alone takes 10, 12 and 15 days, respectively to complete a task. FORMULA USED: Time = Work / Efficiency CALCULATION: Saral, Ravi and Karan alone takes 10, 12 and 15 days Efficiency of Saral $= \frac{1}{10}$ units Efficiency of Ravi $= \frac{1}{12}$ units Efficiency of Karan $= \frac{1}{15}$ units Suppose the number of days taken to complete the task is ‘a’. Saral worked for 2 days, Ravi worked for (a - 3) days and Karan worked for a days. Now, $\frac{2}{10} + \frac{a-3}{12} + \frac{a}{15} = 1$ $\Rightarrow \frac{1}{5} + \frac{a}{12} - \frac{1}{4} + \frac{a}{15} = 1$ $\Rightarrow \frac{3a}{20} = 1 + \frac{1}{20}$ $\Rightarrow \frac{3a}{20} = \frac{21}{20}$ ⇒ a = 7 ∴ Number of days taken to complete the task = 7 days