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jmc

counting and probability junior

Problem

What number is directly above in this array of numbers?
(A)
(B)
(C)
(D)
Solution
Notice that a number in row is less than the number directly below it. For example, , which is in row , is less than the number below it, . From row 1 to row , there are numbers in those rows. Because there are numbers up to the 12th row, is in the row. The number directly above is in the 11th row, and is less than . Thus the number directly above is .
Final answer
C