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Mathematics

Where will the hour hand of a clock stop if it starts from

(i) 6 and turns through 1 right angle?

(ii) 8 and turns through 2 right angles?

(iii) 10 and turns through 3 right angles?

(iv) 7 and turns through 2 straight angles?

Lines & Angles

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Answer

One complete revolution of the hour hand = 12 hours.

1 right angle = 14\dfrac{1}{4} of a revolution = 14×12\dfrac{1}{4} \times 12 = 3 hours.

1 straight angle = 12\dfrac{1}{2} of a revolution = 12×12\dfrac{1}{2} \times 12 = 6 hours.

(i) Starting from 6 and turning through 1 right angle (3 hours, clockwise): 6 → 7 → 8 → 9

∴ The hour hand will stop at 9.

(ii) Starting from 8 and turning through 2 right angles (6 hours, clockwise): 8 → 9 → 10 → 11 → 12 → 1 → 2

∴ The hour hand will stop at 2.

(iii) Starting from 10 and turning through 3 right angles (9 hours, clockwise): 10 → 11 → 12 → 1 → 2 → 3 → 4 → 5 → 6 → 7

∴ The hour hand will stop at 7.

(iv) Starting from 7 and turning through 2 straight angles (12 hours, clockwise): This is one complete revolution.

∴ The hour hand will stop at 7 (same position).

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