2024 AMC 10B Problem 1

Attempt Problem 1 of the 2024 AMC 10B below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2024 AMC 10B solutions, or check the answer key.

All problems are used with official legal permission of the Mathematical Association of America (MAA).

1.

In a long line of people arranged left to right, the 10131013th person from the left is also the 10101010th person from the right. How many people are in the line?
20212021
20222022
20232023
20242024
20252025
Answer: B
Concepts:basic counting
Small hint:
There are 10121012 people to the left of this person and 10091009 to the right
Big hint:
Add the two counts, but do not count this one person twice
Solution:
There are 10121012 people to the left of this spot and 10091009 to the right. Add those two groups plus the person themselves: 1012+1009+1=2022.1012 + 1009 + 1 = 2022. Or, just as fast, the two positions overlap on one person, so 1013+1010−1=2022.1013 + 1010 - 1 = 2022. Thus, B is the correct answer.
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