Roman numerals to 100
Read Roman numerals to 100 (I to C) and understand that the numeral system changed over time to include zero and place value
What a learner can do afterwards
- Read and write Roman numerals I, V, X, L, C and combinations up to 100
- Convert between Roman numerals and Hindu-Arabic numerals (e.g. XLIV = 44)
- Explain that Roman numerals have no zero and no place-value system
The lesson
Long ago, the Romans wrote numbers using letters instead of digits. I means 1, V means 5, X means 10, L means 50, and C means 100. You build bigger numbers by combining these letters.
Two rules control every Roman numeral. If a smaller letter comes after a bigger one, add it: VI is 5 + 1, which is 6. If a smaller letter comes before a bigger one, subtract it: IV is 5 - 1, which is 4.
Look at XLII. Split it into parts. XL is a 10 before a 50, so subtract: 50 - 10 = 40. II is 1 + 1 = 2. Put the parts together: 40 + 2 = 42.
Roman numerals never had a zero, and a letter always means the same amount no matter where it sits. X is always 10, first, middle, or last. That is very different from the place value you know, where a digit's position changes what it is worth.
Roman numerals use letters like I, V, X, L, and C added or subtracted together, with no zero and no place value.
Watch it
Where it sits
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Where this leads
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8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.