Question

Four different electronic devices make a beep after every 30 minutes, 1 hour, 1hour & 30minutes, 1 hour & 45 minutes respectively. All the devices beeped together at 12 noon. They will again beep together at _______ ? And who ?

(A) 12 midnight (B) 3 a.m (C) 6 a.m (D) 9 a.m

Please tell me fast monday is my IMO International maths olmpiyad

Answer 1

First one beeps every 30 min.
Second one beeps every hour = 60min.
Third one at every 1.5 hour = 90min.
Fourth one every 1 hour 45 min = 105 min.

LCM of 30,60,90 and 105 is 1260.
So the devices beep together every 1260 min
1260 min = 21 hours. Thus they beep together every 21 hours after 12 noon.

So we check which of the timings fit.

12 noon + 21 hours= 9 am.

Hence the devices beep together next at 9 am.

Answer 2

Answer:

Step-by-step explanation:

According to question,

First electronic devices beeps after every 30 min.

Second electronic devices beeps after every 60min (1 hour).

Third electronic devices beeps after every 90min (1hour & 30minutes).

Fourth electronic devices beeps after every 105min (1hour & 45minutes).

All the devices beeped together = LCM of 30,60,90 and 105

                                                        = 1260

So all the devices beep together in every 1260 min.

1260 min = 21 hours. Thus they beep together every 21 hours after 12 noon.

12 noon + 21 hours = 9 am.

Hence the devices beep together next at 9 am.