Bianca is painting her room. She plans to paint the ceiling, the door, and the walls all the same color. She is not going to paint her floor. Her room is a rectangular prism shape whose floor is 10 ft by 15 ft. Her walls are 9 ft high.
How many total square feet will Bianca paint? square feet

Justification:

As told in the statement, n stands for the number of bits, and  is the highest number of ways n bits can be arranged in the system.

Now, Antonio wants to show that the character can collect one less key than that. So, that number is less 1, which is what the formula - 1 states.