A can do a piece of work in 4 days and B can complete

A can do a piece of work in 4 days and B can complete the same work in 12 days. What is the number of days required to do the same work together.

  1. 2 days
  2. 3 days
  3. 4 days
  4. 5 days

Answer

Tip: If you can try to remember the percentage reciprocals of the first 20 numbers, it will really speed up your calculations.

For e.g (1/2) = 50 %, (1/3) = 33.33 %, (1/ 6) = 16.66% and so on

Now, A's 1 day's work or efficiency = 1 / 4 = 25%

B's efficiency = 1 / 12 = 8.33%

So, total efficiency = (25 + 8.33) % = 33.33% 

So, total days required = 100 / 33.33 = 3

The correct option is B.