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in Mathematics by (18.1k points)
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A certain 12-hour digital clock displays the hour and the minute of a day. Due to a defect in the clock whenever the digit 1 is supposed to be displayed it displays 7. What fraction of the day will the clock show the correct time?

(a) 1/2

(b) 5/8

(c) 3/4

(d) 5/6

1 Answer

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Best answer

 Answer is : (a) 1/2

Digit 1 appears in 1, 10, 11, and 12 in hour.

∴ The clock will show the incorrect time between 1-2, 10-11, 11-12, 12-1 day and night both incorrect time (8 x 60) = 480 min

Digit l appear in minutes 1, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 31, 41, 51 = 15 min

∴ It will shows the incorrect time = 16 x 15 = 240 min

Total incorrect time = 240+480 = 720 min

Correct time = 24 x 60 - 720

Fraction of correction time

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