1991 AMC 8 Problem 6

Below is the professionally curated solution for Problem 6 of the 1991 AMC 8, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 1991 AMC 8 solutions, or check the answer key.

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Concepts:systematic listingextremal argument

Difficulty rating: 800

6.

Which number in the array below is both the largest in its column and the smallest in its row? (Columns go up and down, rows go right and left.)

10643211714108834591341512182593\begin{array}{ccccc} 10 & 6 & 4 & 3 & 2 \\ 11 & 7 & 14 & 10 & 8 \\ 8 & 3 & 4 & 5 & 9 \\ 13 & 4 & 15 & 12 & 1 \\ 8 & 2 & 5 & 9 & 3 \end{array}

11

66

77

1212

1515

Solution:

The largest entry in each column is 1313 (column 11), 77 (column 22), 1515 (column 33), 1212 (column 44), and 99 (column 55).

Of these, only 77 is the smallest number in its own row (row 22 is 11,7,14,10,811, 7, 14, 10, 8).

Thus, the correct answer is C .

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