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SSC CGL Tier 1 :: Quantitative Aptitude QA Test 62

Quantitative Aptitude » QA Test 62 » General Questions - Discussion

1 .


The traffic lights at three different road crossings change every 21 seconds, 63 seconds and 105 seconds respectively. If they all change simultaneously at 9 : 15 : 00 AM, at what time will they again change simultaneously?

[ A ]    9 : 20 : 15 AM right
[ B ]    8 : 20 : 30 AM
[ C ]    9 : 17 : 36 AM
[ D ]    9 : 18 : 15 AM
Answer : Option A
Explanation :
Interval of change = (LCM of 21,63,105) = 315 sec

So, the lights will again change simultaneously after every 315 sec,ie 5 min 15 sec.

Hence , next simultaneous change will take place at 9:20 :15 AM.
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