Convert the whole number to a fraction with the same denominator as the other fraction.

$$
1 = \frac{4}{4}
$$

$$
\frac{4}{4} - \frac{1}{4} = \frac{4-1}{4} = \frac{3}{4}
$$
The answer is $\boxed{\frac{3}{4}}$.

One hundred two thousand = 102,000  
Five hundred and ninety two = 592

$$
102,000 + 592 = 102,592
$$
The answer is $\boxed{102,592}$.

$$
\frac{1}{2} = \frac{1 \times 5}{2 \times 5} = \frac{5}{10}
$$

Since $5 > 1$, it follows that $\frac{5}{10} > \frac{1}{10}$.  
Therefore, $\frac{1}{2} > \frac{1}{10}$.  
The answer is $\boxed{>}$.

$129 - 123 = 6$  
$135 - 129 = 6$  
$141 - 135 = 6$  
$147 - 141 = 6$

The operation used is $\boxed{\text{addition of } 6}$.

CM = 900 (C before M means $1000 - 100$)  
XXX = 30 ($10 + 10 + 10$)  
IX = 9 (I before X means $10 - 1$)

$$
900 + 30 + 9 = 939
$$
The number in words is $\boxed{\text{Nine hundred thirty-nine}}$.

$1000 = M$  
$5 = V$

$$
1000 + 5 = MV
$$
The Roman numeral is $\boxed{MV}$.