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A word-and-number arrangement machine, when given an input line of words and numbers, rearranges it in steps. The elements it has not yet touched always stand together at the left of the line, in their original order. In each step the machine takes one untouched element and places it at the extreme right end of the line: in odd-numbered steps it takes the leftmost untouched element, and in even-numbered steps it takes the rightmost untouched element. The machine stops once no untouched element is left.
Input: 73 quartz 19 raven 84 sable 32.
In Step 4 of the above arrangement, which element stands immediately to the right of "84"?

Competition practiceInput-Output
  • Araven
  • B73
  • C32
  • Dsable

Step-by-Step Solution

Step 1 (leftmost, 73): quartz 19 raven 84 sable 32 73. Step 2 (rightmost untouched, 32): quartz 19 raven 84 sable 73 32. Step 3 (leftmost, quartz): 19 raven 84 sable 73 32 quartz. Step 4 (rightmost untouched, sable): 19 raven 84 73 32 quartz sable. So the line reads 19 raven 84 73 32 quartz sable, and 84 is followed immediately by 73. Raven stands immediately to its left; 32 is one place further on; and sable, only just taken, sits at the very end.
Answer: B) 73

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