Three bulbs red, green and yellow flash at intervals of 80 seconds, 90 seconds and 110 seconds. All three flash together at 8:00 am. At what time will the three bulbs flash altogether again?
a)at 9 o'Clock
b)at 10:12
c)at 9:12
Answers
SOLUTION
TO CHOOSE THE CORRECT OPTION
Three bulbs red, green and yellow flash at intervals of 80 seconds, 90 seconds and 110 seconds. All three flash together at 8:00 am. At what time will the three bulbs flash altogether again
a) at 9 o'Clock
b) at 10 : 12
c) at 9 : 12
EVALUATION
Here it is given that three bulbs red, green and yellow flash at intervals of 80 seconds, 90 seconds and 110 seconds
We now find the LCM of 80 , 90 , 110
80 = 2 × 2 × 2 × 2 × 5
90 = 2 × 3 × 3 × 5
110 = 2 × 5 × 11
LCM
= 2 × 2 × 2 × 2 × 3 × 3 × 5 × 11
= 7920
Now 3600 seconds = 1 hour
∴ 7920 seconds
= 2 hour 720 seconds
= 2 hour 12 minutes
Since all three flash together at 8 : 00 am
Hence the time when the three bulbs flash altogether again
= 8 : 00 am + 2 hour 12 minutes
= 10 : 12 am
FINAL ANSWER
Hence the correct option is b) at 10 : 12
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10:12 is the answer... hope it helps u