How much water should be added to a 36ml of 20% alchohol solution to reduce the concentration to 18%?

N - ml of alcohol

n1(alcohol in 20%) = n1(alcohol in 18%) 

0.20*36 ml = 0.18 *x ml

x= 0.20*36/0.18  = 20*36/18= 40 ml of 18% solution

We had 36 ml, we will get 40 ml,
so we need to add 
40 ml - 36 ml = 4 ml of water.

The  grandmother cell  is a hypothetical  neuronthat represents a complex but specific concept or object.[1]  it activates when a person "sees, hears, or otherwise sensibly discriminates"[2]  a specific entity, such as his or her grandmother. the term was in use at least as early as 1966 amongst staff and students in the department of experimental psychology, university of cambridge, england. a similar concept, that of the  gnostic neuron, was proposed two years later