# three ways to input values 

pv_f<-function(fv,r,n)fv/(1+r)^n

# method 1: 
   pv_f(100,0.08,1)

# [1] 92.59259


# Method  2: keyword approach

   pv_f(fv=100,n=1,r=0.08)

   pv_f(n=1,r=0.08,fv=100)

   pv_f(fv=100,r=0.08,n=1)

# Method 3: mixed approach
#           consider the keywords first
#           then consider the order

 pv_f(n=1,100,0.08)
#[1] 92.59259

 pv_f(fv=100,0.08,1)
# [1] 92.59259