Question

A Mason completes 0.2 portion of the wall in first day. For next day onwards he completes 0.1 portion of the wall everyday. In How many days the Mason will complete the construction of the wall?

Answer 1

The maison could have completed the construction in 10 days if he completed 0.1 i.e. 1/10 portion of wall in 1 day. But because on the 1st day he completed 0.2 i.e. 2/10 portion of the wall, he did 2 days work together. This means that overall he will complete the construction of the wall in 9 days in place of 10.
(2/10 + 1/10 + 1/10 + 1/10 + 1/10 + 1/10 +1/10 + 1/10 + 1/10) = 10/10 i.e. 1 which is the total work.

Answer 2

Solution :-

Since the mason completes 0.2 portion of the wall on first day 
So, 2/10th part is completed on first day.
And, he completes o.1 portion of the wall everyday
So, everyday he completes 1/10 portion of the wall.
In 8 days he completes (1*8)/10 portion of the wall 
That will be 8/10.
Total = 2/10 + 8/10 = 1
Total days taken to construct the wall = (1 + 8) days 
= 9 days
Therefore, he will take 9 days to complete the construction of the wall.