If a patch of moss doubles in size everand the wall is covered in 54 days, hjow long would it take for the patch to cover half the wall

Question

On a case wall ther is a patch of moss. Everyday the patch doubles in size. If it takes 54 days for the patch to cover the entire wall, hjow long would it take for the patch to cover half the wall

Answer 1

We know that the moss doubles everyday and it gets covered in 54 days. we want to know when the wall is 1/2 covered. 

 

So this means on day 53 we have half the wall covered. 

Answer 2

Madhuri simply applied basic logic without setting up an equation.  If the patch doubles in size every day then the day before it covered the full wall it had to be covering half the wall.  Thus, it covers half the wall on day 53.