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# Explanation

### Explanatory Answer

**Method 1**

Here the total work to build a floor is considered as 1 unit.

Let the Efficiency of worker of working on 1^{st} day = x

Thus efficiency of worker working on 2^{nd} day, 3^{rd} day, 4^{th} day and 5^{th} day is 2x, 4x, 8x and 16x respectively.

From the Line graph we can see it took a total of 5 days to build 4^{th} floor.

- x + 2x + 4x + 8x + 16x = 1
- x = 1/31

The efficiency of the worker working on second day is 2/31.

Thus the worker working on second day will take 31/2 days i.e. 15.5 days to complete the 4^{th} floor working alone.

Increase in time = 15.5 – 5 = 10.5 days

**Method 2**

Let the worker working on first day complete 1 unit of work each day.

Then the worker working on 2^{nd} day, 3^{rd} day, 4^{th} day, 5^{th} day completes 2 units, 4 units, 8 units, 16 units of work each day.

From the Line graph we can see it took a total of 5 days to build 4^{th} floor.

Thus total units of work required to complete the 4^{th} floor = 1+2+4+8+16 = 31 units

The worker working on second day will take 31/2 days = 15.5 days.

Increase in time = 15.5 – 5 = 10.5 days