Question

Four people clap after every 20 minutes, 30 minutes, 40 minutes and 50 minutes respectively. All of them clapped together at 10:00 am. Then they will again clap together at ______

• A. 3 pm
• B. 5 pm
• C. 6 pm
• D. 8 pm

Hint:

Find the LCM of the four time gaps and convert it to hours.

Answer 1

The Correct Option is D

Step 1: Combine the intervals two at a time.
Start with 20 and 30. Their LCM is 60, since 60 is the smallest number both divide evenly.

Step 2: Bring in the next interval.
Now combine 60 with 40. Checking multiples of 60 (60, 120), 120 is divisible by 40, so the LCM of 20, 30, 40 is 120.

Step 3: Bring in the last interval.
Combine 120 with 50. Checking multiples of 120 (120, 240, 360, 480, 600), 600 is the first one divisible by 50, so the overall LCM is 600 minutes, which is 10 hours.

Final Answer:
Adding 10 hours to 10:00 am gives the same answer, 8 pm. \[ \boxed{8 \text{ pm}} \]