A mechanical grandfather clock is at present showing 7 hours 40 minutes 6 seconds. Assuming that it loses 4 seconds in every hour, what time will it show after exactly $$6\frac{1}{2}$$ hours ?

$$\eqalign{ & {\text{Time lost in }}6\frac{1}{2}{\text{ hours}} \cr & = {\text{ }}\left( {6\frac{1}{2} \times 4} \right)\sec \cr & = 26\sec \cr} $$
Correct time after $${\text{6}}\frac{1}{2}$$ hours
= 7 hours 40 minutes 6 seconds + 6 hours 30 minutes
= 14 hours 10 minutes 6 seconds
Time show by the clock
= 14 hours 10 minutes 6 seconds - 26 sec
= 14 hours 9 minutes 40 seconds