Page 26 - Start Up Mathematics_4

In modern Roman numeral system, for large numbers a bar is placed above the base numeral
indicating multiplication by 1,000, although the ancient Romans themselves often just used
M for it.

V Five thousand
Maths Fun
X Ten thousand

How can half of
L Fifty thousand XII be 7?
C One hundred thousand

D Five hundred thousand

M One million

Conversion of Roman Numeral to Hindu-Arabic Numeral

1. If a smaller number is to the left of a larger number, subtract the value of the smaller
number from the larger number.
Consider the number IX. Since I < X, 10 – 1 = 9. Therefore, IX = 9.
Also, in XL, X < L. Therefore, XL = 50 – 10 = 40.
2. Subtract only the values of letters I, X and C. Values of V, L and D cannot be subtracted.
Consider the numeral 45.

45 = XLV [(50 – 10) + 5] 45 ≠ VL (50 – 5)

3. Subtract the value of only a single smaller numeral from a single bigger numeral. In
other words, you can subtract only once from a numeral.
Consider the numeral 8.
8 = VIII (5 + 3) 8 ≠ IIX (10 – 1 – 1)

4. Do not subtract a numeral from another numeral which is more than 10 times greater,
i.e., I can be subtracted from V and X but not from L, C, D and M. Similarly, X can be
subtracted from L and C but not from D, M and so on.

5. If a smaller number is to the right of a larger number, add the value of the smaller
number to the larger number.
Consider the number XI.

Since X > l, 10 + 1 = 11. Therefore, XI = 11.
Remember
6. If the number has more than two letters, add the
value of each letter to find the number. • We cannot repeat a symbol
Consider the number LXVIII. more than 3 times to write a
Roman numeral.
LXVIII = 50 + 10 + 5 + 1 + 1 + 1 • Symbols V, L and D cannot

= 68 be repeated at all.

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