Writing a number with landmark numbers
Take the largest landmark that fits, again and again.
27 in landmarks
The landmark numbers are 1, 5, 10, 50, 100, 500, 1000. To write 27, we must choose which landmarks to take.
Which landmark would you take first to write 27?
What this lesson covers
The idea
A number is written by taking as many of the largest landmark number as possible, then as many of the next smaller one, and so on, and writing each landmark's symbol as many times as it is used.
27 in landmarks
The landmark numbers are 1, 5, 10, 50, 100, 500, 1000. To write 27, we must choose which landmarks to take.
Which landmark would you take first to write 27?
- X (10), as many as fit
- I (1), as many as fit
- V (5), as many as fit
Build the numbers
Tap landmarks to take them until you have written the number exactly. Always take the largest landmark that still fits before a smaller one.
As many of the largest as possible
A number is written by taking as many of the largest landmark number as possible, then as many of the next smaller one, and so on, and writing each landmark's symbol as many times as it is used.
27 = 10 + 10 + 5 + 1 + 1 gives XXVII.
2367 = 1000 + 1000 + 100 + 100 + 100 + 50 + 10 + 5 + 1 + 1 gives MMCCCLXVII.
Notes
A number is written by taking as many of the largest landmark number as possible, then as many of the next smaller one, and so on, and writing each landmark's symbol as many times as it is used.
Check yourself
To write 27, how many X (10) do you take before moving on to a smaller landmark?
Answer: 2
27 = 10 + 10 + 7. Two Xs, then the remaining 7 is written with V, I and I: XXVII.
You are writing 367. Which landmark do you take first?
How many symbols are in the Roman numeral for 1367 (count every letter written)?
Answer: 9
1367 = 1000 + 100 + 100 + 100 + 50 + 10 + 5 + 1 + 1, so it is written MCCCLXVII, with 9 letters.
Which method writes a number with landmark numbers?
- C (100) — correct. Yes! 100 is the largest landmark that fits in 367. Take three of them.
- L (50). 50 fits, but 100 is larger and fits too. Take the largest landmark first.
- D (500). 500 is more than 367, so it does not fit.
- X (10). 10 fits, but larger landmarks fit too. Start with the largest.
- Take as many of the largest landmark as possible, then the next smaller, and so on — correct. Yes! Then write each landmark symbol as many times as you used it.
- Take as many 1s as possible first. That gives a tally of 1s. Start from the largest landmark instead.
- Take the smallest landmark first and work upwards. That does not work well. Start with the largest landmark that fits.