M=1000
D=500
C=100
L=50
X=10
V=5
I=1

CDXLVII+XVI/IV

To change CDXLVII from Roman to Arabic numerals, 

first we group it as follows:

Going left to right,

C to D is an increase
D to X is a decrease
X to L is an increase
L to V is a decrease
V to I is a decrease
I to I is the same

Group the pairs which show an increase or "the same" going 
left to right.

(CD)(XL)V(II)

The C BEFORE the D means to SUBTRACT 100 from 500 and get 400.
The X BEFORE the L means to SUBTRACT 10 from 50 and get 40.
The V just means 5. (Ungrouped letters just get their value)
The I and the I are the same, so we ADD 1+1 and get 2.

So CDXLVII = 400+40+5+2 = 447

To figure out XVI

X to V is a decrease
V to I is a decrease

So there are no increases to group, so we just add their 
individual values:

XVI = 10+5+1 = 16

To figure out IV

I to V is an increase, so we group them as

(IV)

Since the I is before the V, we subtract 1 from 5 and get 4.

CDXLVII+XVI/IV

447+16/4

447+4 = 451

Edwin