Roman numerals need five signs up to 100. I is 1, V is 5, X is 10, L is 50 and C is 100. Next to each other they add up, so LXII is 50 + 10 + 1 + 1, which makes 62.
If a smaller sign comes BEFORE a bigger one, it gets subtracted. So XL is 50 − 10 = 40 and XC is 100 − 10 = 90.
The stonemason is paid for every symbol he carves into the stone, not for how big the number is. Write the number in Roman numerals, count the symbols and multiply them by the pay.
For parents
What does this exercise practice?
The stonemason order links writing Roman numerals with the times tables and trains children to tell a quantity apart from the way it is written. The price depends on the notation, not on the value.
Common pitfalls
Almost every child first guesses that the biggest number is the most expensive. That is exactly what does not hold here. 100 is a single C and therefore the cheapest number in the table, while 38 needs seven symbols as XXXVIII. Work it out first, then answer.
How to practice at home
Write your age in Roman numerals and count the symbols. Who in the family would have the most expensive stone? Usually it is not the oldest person.
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