Question

three bulbs red,green and yellow flash at internals of 80 seconds,90 seconds and 110 seconds. all three flash together at 8:00 am.at what time the three bulbs flash altogether againthree bulbs red,green and yellow flash at internals of 80 seconds,90 seconds and 110 seconds. all three flash together at 8:00 am.at what time the three bulbs flash altogether again

Answer 1

Solution :-

The next time three bulbs flash together after time LCM of 80 seconds, 90 seconds and 110 seconds .

So, finding LCM of 80 seconds, 90 seconds and 110 seconds we get,

→ 80 = 2 * 2 * 2 * 2 * 5

→ 90 = 2 * 3 * 3 * 5

→ 110 = 2 * 5 * 11

then,

→ LCM = 2 * 2 * 2 * 2 * 3 * 3 * 5 * 11 = 7920 seconds .

now,

→ 60 seconds = 1 minute

→ 7920 seconds = (1/60) * 7920 = 132 minutes .

now,

→ 60 minutes = 1 hour

→ 120 minutes = 2 hours .

therefore,

→ All three flash together at = 8 : 00 AM + 2 : 12 = 10 : 12 AM (Ans.)

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Answer 2

Three bulbs flash altogether again at 10:12 am

Given :

• 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.

To find : The time when the three bulbs flash altogether again

Solution :

Here it is given that three bulbs red, green and yellow flash at intervals of 80 seconds, 90 seconds and 110 seconds

We now find the LCM of 80 , 90 , 110

80 = 2 × 2 × 2 × 2 × 5

90 = 2 × 3 × 3 × 5

110 = 2 × 5 × 11

LCM

= 2 × 2 × 2 × 2 × 3 × 3 × 5 × 11

= 7920

Now 3600 seconds = 1 hour

∴ 7920 seconds

= 2 hour 720 seconds

= 2 hour 12 minutes

Since all three flash together at 8 : 00 am

Hence the time when the three bulbs flash altogether again

= 8 : 00 am + 2 hour 12 minutes

= 10 : 12 am

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