Subject: General Aptitude · Chapter: H.C.F. and L.C.M. of Numbers · Exam: · Marks: · Difficulty:
Four different electronic devices make a beep after every 30 minutes, 1 hour, $1 \frac{1}{2}$ hour and 1 hour 45 minutes respectively. All the devices beeped together at 12 noon. They will again beep together at
(a)12 midnight
(b)3 a.m.
(c)6 a.m.
(d)9 a.m.
Answer
Answer (as printed): D
Explanation
Interval after which the devices will beep together $$\begin{aligned} & =(\mathrm{L} . \mathrm{C} . \mathrm{M} . \text { of } 30,60,90,105) \mathrm{min} . \\ & =1260 \mathrm{min}=21 \mathrm{hrs} . \end{aligned}$$ So, the devices will again beep together 21 hrs. after 12 noon i.e., at 9 a.m.