Subject: General Aptitude · Chapter: H.C.F. and L.C.M. of Numbers · Exam: 2016 · Marks: · Difficulty:
The traffic lights at three different signal points change after every 45 seconds, 75 seconds and 90 seconds respectively. If all change simultaneously at 7 : 20 : 15 hours, then they will change again simultaneously at
(a)7 : 28 : 00 hours
(b)7 : 27 : 45 hours
(c)7 : 27 : 30 hours
(d)7 : 27 : 50 hours
Answer
Answer (as printed): B
Explanation
5 | 45-75 - 90 ; 3 | 9-15 -18 ; 3 | 3-5 - 6 ; 1-5 - 2 $$\Rightarrow 5 \times 3 \times 3 \times 5 \times 2=450$$ LCM of 45, 75, 90 is 450 ∴ Traffic lights will change simultaneously after 7 minutes 30 seconds i.e. at 7 : 27 : 45 hours.
Explanation as extracted from the printed page; notation may be imperfect.