Question

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 together ?
i.) 9:00 am
ii.) 9:12 am
iii.) 10:00 am
iv.) 10:12 am
this answer is answer 4...
but I want answer briefly​

Answer 1

Answer:

10:12 am

Step-by-step explanation:

LCM of 80, 90, 110 = 7920 sec

Convert into hour.

= 7920 ÷ 3600      ∵[ 1 hour = 3600 sec]

= 2.2 hour

So, after (8+2.2) am, all bulbs flash together.

2.2 hour means,  

2 hour + 0.2 hour    

0.2 hour = 12 mins      ∵ [0.1 hour means 6 mins]

So, 2 hour and 12 mins than 8:00 am

= 8 + 2 hour and 12 mins

= 10:12 am