Q:

True or False: A two full F/stop change to either side of the starting F/stop will either double or half the amount of light from the original F/stop

Explain.  
A two full F/stop change to either side of the starting F/stop will either double or half the amount of light from the original F/stop. 

A:

False. Going from f/2 to f/2.8 will halve the light; going from f/2 to f/4 will quarter it.

