Rahul put his timepiece on the table in such a way that at 6 P.M., the hour…

20242023

Rahul put his timepiece on the table in such a way that at 6 P.M., the hour hand points to North.

In which direction will the minute hand point at 9:15 P.M.?

  1. A.

    South

  2. B.

    North

  3. C.

    East

  4. D.

    West

Attempted by 4 students.

Show answer & explanation

Correct answer: D

In a direction-sense problem built on a clock face, the dial's four quarter-marks (12, 3, 6, 9) are first assigned default compass directions as if the clock hangs in its usual reading position — 12 to North, 3 to East, 6 to South, 9 to West. If the physical clock is turned so that one of these marks now points a different compass direction, every mark on the dial turns together by that same angle, so each mark keeps its position relative to the others; only the compass label attached to each mark shifts.

  1. At 6 P.M. the hour hand rests exactly on the 6 o'clock mark. The problem states this mark points North, whereas its default direction is South — a difference of 180 degrees, so the whole dial is rotated 180 degrees from the default mapping.

  2. Rotating every default direction by 180 degrees swaps each mark with its opposite: 12 (default North) now points South, 6 (default South) now points North (confirming the given fact), 3 (default East) now points West, and 9 (default West) now points East.

  3. At 9:15 P.M., the minute hand has moved a quarter of the way round the dial from the top, i.e. it rests on the 3 o'clock mark.

  4. From step 2, the 3 o'clock mark now points West, so the minute hand points West.

As a check, opposite marks on a clock always point in opposite compass directions. 12 and 6 are opposite marks: 6 is North (given), so 12 must be South, matching the 180-degree rotation derived above. Likewise 3 and 9 are opposite marks, so if 3 is West then 9 must be East, consistent with step 2. This confirms the result: West.

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