510 in Roman numerals

510 in Roman numerals is DX.

Pick any whole number from 1 to 3,999.

510 = \text{DX}

How to work it out

1
Take the biggest Roman value that fits, write its letter, subtract it, and repeat.
2
Here: 500 (D) + 10 (X) = 510.
3
Joined together: DX. (Four of the same letter in a row is never used: 4 is IV, 9 is IX, 40 is XL, 90 is XC, 400 is CD, 900 is CM.)

Value	Letters
500	D
10	X

What is 510 in Roman numerals?

DX.

How do you read DX?

DX = 500 + 10 = 510.