Skip to content
Related Articles

Related Articles

Puzzle 32| (Completion of Task)

View Discussion
Improve Article
Save Article
  • Difficulty Level : Easy
  • Last Updated : 11 May, 2021

A man is allocated a task. He doubles the task done everyday. If the man completely does the task in 18 days, how many days did it take for the man to complete 25% of the task? 

Answer: 16 

100% of task = 18 days 

As he doubles the task everyday. So, 

50% of task = 17 days 

25% of task = 16 days. 

Alternative Solution :

Let the amount of work the man did on first day be x and total work to be done be S.

As the amount of work he did on next day would be 2 times of it’s previous day, we can write amount of work he did on 2nd day as ‘2x’, 3rd day ‘4x’, 4th day ‘8x’ and so on….

We can write it as a GP as follows : 

S = x+2x+4x+8x+….. (till 18th day)

S = x*(218-1)/(2-1)    [Formula of summation of GP S=a(rn-1)/(r-1)]

S=x*(218-1)    –   equation (1)

According to ques we have to find the day when he would complete 25% of the total work, then ‘S’ becomes ‘S/4’

We can write the expression as

S/4 = x+2x+4x+8x+….  (till nth day)



Substituting value of S from equation (1)


On simplifying



2n+2=218+3    (2n*4=2n*22=2n+2)

We can neglect 3 in comparison of 218



n=16 days

So answer is 16 days.

This article is contributed by Vikash Kumar and Hardik Mittal. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above

My Personal Notes arrow_drop_up
Recommended Articles
Page :

Start Your Coding Journey Now!