AMC 10 Step by Step
2025 AMC 10BProblem 3P1-10~3 minPrint

A Pascal-like triangle has 1010 as the top row and 1010 followed by 11 as the second row. In each subsequent row the first number is 1010 , the last number is 11 , and, as in the standard Pascal's Triangle, each other number in the row is the sum of the two numbers directly above it. The first four rows are shown below:

10101101111021121\begin{array}{ccccccc} &&&10&&&\\ &&10&&1&& \\ &10&&11&&1& \\ 10&&21&&12&&1 \\ \end{array}

What is the sum of the digits of the sum of the numbers in the 1111 th row?

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Problem © Mathematical Association of America (MAA), American Mathematics Competitions. Reproduced for non-commercial educational use. Solution and commentary are original to this site.