Question

Two alarms ring simultaneously at 3am. The first alarm rings every 20 minutes while the second alarm rings every hour. What time will the two alarms ring at the same time for the third time.

Answer 1

First alarm ring after every 20 min
2nd after 60 min
LCM of 20,60 is= 120 min= 2hrs
So
Again at 5am they ring together.

Answer 2

Answer:

Two alarm ring simultaneously for third time at 5 AM.

Step-by-step explanation:

Given:

Time when Two alarm ring simultaneously for first time = 3 AM

First alarm rings every 20 minutes.

Second alarm rings every 1 hr = 60 minutes.

To find: Time when Two alarm ring simultaneously for third time.

We find LCM of the 20 and 60

20 = 2 × 2 × 5

60 = 2 × 2 × 3 × 5

LCM = 2 × 2 × 3 × 5 = 60

So, Both alarm ring simultaneous after every 60 minutes that is 1 hr.

Time when both alarm ring simultaneous for third time = 3 + 2 = 5 AM

Therefore, Two alarm ring simultaneously for third time at 5 AM.