Question

A clock hung on a wall has marks instead of numerals on its dial on the adjoining wall there is a plane mirror and the image of the clock in the mirror indicates the time $7 : 10$. Then the time on the clock is:

• A. 7:10
• B. 4:50
• C. 5:40
• D. 10:07

Answer 1

Answer: (B)

4:50

Answer 2

In a plane mirror the image undegoes depth inversion hence, the time on the image is as much ahead of $12\, h\, 0\, \min$ as the time on actual clock is behind $12\, h\, 0 \,\min$.
Time on the actual clock $=7 \,h\, 10\, m$.
Time on the image clock
$=(12 \,h$ and $0 \,\min )-(7\, h$ and $10\, \min )$
$\therefore 4\, h$ and $50\,\min$