Question

Q:21. Three neon signs are turned on at the same time. The
first one blinks after every 10 seconds, the second one
after every 20 seconds and the third one after every 25
seconds. When will they blink together again they
blinked last at 9:00 pm?​

Answer 1

Answer:

10:40 p.m

Step-by-step explanation:

First one: 9:10, 9:20, 9:30, 9:40, 9:50, 10:00, 10:10, 10:20, 10:30, 10:40

Second one: 9:20, 9:40, 10:00, 10:20, 10:40

Third one: 9:25, 9:50, 10:15, 10:40

Answer 2

Answer:

The three neon signs blinked together after 9.00 pm will be at 9.16 pm

Step-by-step explanation:

Given:

• The first neon signs blinks after 10 seconds.
• The second one signs blinks after 20 seconds.
• The third one signs blinks after 25 seconds.

To find:

The time at which the three neon signs will blink together after 9:00 pm

Solution:

• Find the The least common multiple of 10, 20, 25
• L C M of 10, 20, 25 is 100
• Therefore after every 100 seconds they will blink together at the same time.

60 seconds = 1 minute

100 seconds = 60 seconds + 40 seconds

                     = 1 minute 40 seconds

• So after 1 minute 40 seconds the neon signs will blink together.
• The neon signs blinked together last at = 9.00 pm
• So, after 1 minute 40 seconds they will blink together at 9 .166 pm

Note: 100 seconds = 1 minute 40 seconds = 1.666667 minutes

Answer : At 9.16 pm the three neon signs will blink together.

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