AMC 10 · 2024 · #1

Grade 4 arithmetic
multi-digit-arithmeticpattern-recognitioncomplementary-counting identify-subproblemseasier-related-problem ↑ Prerequisites: multi-digit-arithmeticorder-of-operations
📏 Short solution 💡 2 insights
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Problem
One person stands in a single line. Counting from the left, they are the 1013th person; counting from the right, they are the 1010th person. How many people are in the whole line?

Pick an answer.

(A)
2021
(B)
2022
(C)
2023
(D)
2024
(E)
2025

AMC 10 2024 problem © Mathematical Association of America (MAA AMC). Reproduced for educational use.

How to solve
Strategy Draw a Diagram

The problem is a position-on-a-line picture: one fixed person, some people to the left, some people to the right. Tool #1 (Draw a Diagram) makes that picture explicit — sketch L L L ... L | P | R R R ... R and the count becomes visible. Tool #7 (Identify Subproblems) cleanly splits the line into three independent pieces — left of the person, the person themselves, right of the person — so we can count each piece and add.

1STEP 1

Sketch the line in three labeled pieces — people on the left, the named person, people on the right — so the total is just their sum.

L L … L_left of P | P | R R … R_right of P
2STEP 2

Count the left side — being 1013th from the left leaves 1012 people before this person.

left of P = 1013 - 1 = 1012 people
3STEP 3

Count the right side — being 1010th from the right leaves 1009 people after this person.

right of P = 1010 - 1 = 1009 people
4STEP 4

Add the three pieces — 1012 + 1 + 1009 — to reach 2022, the whole line.

1012 + 1 + 1009 = 2022 → (B)
Answer
2022
Sanity-check with the shortcut formula: total = (from left) + (from right) - 1 = 1013 + 1010 - 1 = 2022. The -1 removes the double-count of the one person who is named from both sides. Same answer (B). Also, 1013 + 1010 = 2023 is just barely above 2022, so an answer near 2022 is exactly what we expect.
💡Key takeaway

This AMC 10 problem only needs Grade 4 multi-digit addition (and one careful subtract-1 from position counting) that you already know!