A light was seen at intervals of 13 seconds. It was seen for the first time at 1 hr. 54 min. 50 secs. a.m. and the last time at 3 hrs. 17 min. 49 secs. a.m. How many times was the light seen?
(a)360
(b)375
(c)378
(d)384
Answer
Answer (as printed): D
Explanation
$$\begin{array}{lll} \text { Hrs. } & \text { Min. } & \text { Sec. } \\ 3 & 17 & 49 \\ 1 & 54 & 50 \\ \hline 1 & 22 & 59 \\ \hline \end{array}$$ Total time $=(1 \times 60+22) \mathrm{min} .+59 \mathrm{sec}$. $$\begin{aligned} & =(82 \times 60+59) \mathrm{sec} . \\ & =4979 \mathrm{sec} . \end{aligned}$$ ∴ Number of times the light is seen $=\left(\frac{4979}{13}+1\right)=384$.
Explanation as extracted from the printed page; notation may be imperfect.