CAT Quantitative Ability Questions | CAT Permutation, Combination and Probability questions
CAT/2001
Question . 42
A red light flashes 3 times per minute and a green light flashes 5 times in two minutes at regular intervals. If both lights startflashing at the time, how many times do they flash together in each hour?
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Explanatory Answer
Method of solving this CAT Quantitative Ability Question from Permutation, Combination and Probability question
(a) Red light flashes 3 times / min. i.e after every20 seconds.
Green light flashes 5 times in 2 min. i.e. after every24 seconds.
So, they flash together after every 2 minutes= 120 seconds
(L.C.M. of 20 & 24 = 120)
Hence, in 1 hour they flash together 60/2 = 30 times