## pratu043 3 years ago Four bells first begin to toll together and then at intervals of 6, 7, 8 and 9 seconds respectively. Find how many times the bells toll together in two hours and at what intervals they toll together?

1. sauravshakya

First find L.C.M of 6,7,8 and9

2. pratu043

ok. 504.

3. sauravshakya

Are u sure

4. sauravshakya

ya... thats right

5. sauravshakya

So, the four bells will ring afer 540 seconds all together

6. sauravshakya

got it?

7. pratu043

504.

8. sauravshakya

now, 2 hour = ---- seconds

9. pratu043

But it says they ring together at intervals of 6, 7, 8, 9 seconds.

10. pratu043

So what have these numbers got to do with 504?

11. sauravshakya

Since the Four bells first begin to toll together and then at intervals of 6, 7, 8 and 9 seconds respectively

12. sauravshakya

they will ring together after 540 seconds now

13. sauravshakya

14. pratu043

So after that nine seconds, they will ring together after 504 seconds?

15. sauravshakya

nope.....

16. pratu043

Lets say they ring together first at 6.00.00. Then at 6.00.06 6.00.07 6.00.08 6.00.09 right?

17. sauravshakya

nope.....

18. sauravshakya

Let me first expalin the question

19. sauravshakya

there are four bells|dw:1344785837617:dw|

20. sauravshakya

which ring together at first

21. sauravshakya

then BELL A rings after 6 seconds, BELL B rings after 7 seconds , BELL C rings after 8 seconds and BELL D rings after 9 seconds

22. sauravshakya

got it?

23. pratu043

yep i got it now.

24. sauravshakya

so what do u think 540seconds means

25. pratu043

2 hours = 2 * 60 * 60 seconds = 3600 * 2 = 7200 seconds

26. pratu043

The three bells will ring TOGETHER every 504 seconds right?

27. sauravshakya

right

28. pratu043

OK, I know how to do it now. Thanks!!

29. sauravshakya

WELCOMX