Problem 4 · 2022 Math Kangaroo
Easy
Number Theory
place-value
In the 13th century, monks wrote numbers in a special way: for the numbers 1 to 99 they used the signs shown here, or a combination of two of these signs. For example, the number 24 was written one way, 81 another, and 93 another. What did the number 45 look like?
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Answer: D
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Hint 1 of 2
Split 45 into a tens part and a units part: 40 and 5.
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Hint 2 of 2
Combine the sign for 40 with the sign for 5, just as 24 combined the signs for 20 and 4.
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Approach: combine the tens-sign and units-sign for 45
- The system writes a two-digit number by combining one tens sign and one units sign.
- For 45 take the sign for 40 and the sign for 5.
- Putting them together gives the figure shown in D.
- So 45 looks like D.
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