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Pendulum A rings once in 3 seconds and another pendulum B rings 4 times in 7 seconds. If both the pendulums start ringing at the same time, how many times will they ring together in 1 minute?

Pendulum A rings once in 3 seconds and another pendulum B rings 4 times in 7 seconds. If both the pendulums start ringing at the same time, how many times will they ring together in 1 minute? Correct Answer 2

Given:

Pendulum A rings once in 3 seconds 

Pendulum B rings 4 times in 7 second

Calculation:

Pendulum B rings 4 times in 7 second

⇒ Pendulum B rings once in 7/4 second

And, Pendulum A rings once in 3 seconds 

Now, If we take LCM of 3/1 seconds and 7/4 seconds

LCM (3/1, 7/4) = LCM (3, 7)/HCF (1, 4) 

⇒ LCM (3/1, 7/4) = 21/1 = 21

i.e We can say that pendulum A and B ring together at an interval of 21 seconds 

We know that,

1 minute = 60 seconds 

Now, On dividing 60 by 21 seconds we get 

60 = 21 × 2 + 18

∴ Quotient 2 shows that both pendulums ring together twice in 1 minute.

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