LCM and HCF

L.C.M. of 2 , 4 , 5 is 3 9 6

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As we know that ,
LCM of fractions = LCM of numerators HCF of denominators LCM = LCM of 2, 4, 5 HCF of 3, 9, 6 Correct Option: B
As we know that ,
LCM of fractions = LCM of numerators HCF of denominators LCM = LCM of 2, 4, 5 HCF of 3, 9, 6 LCM = 20 3
 Five bells begin to toll together and toll respectively at intervals of 6, 7, 8, 9 and 12 seconds. After how many seconds will they toll together again ?

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Required time = LCM of 6, 7, 8, 9 and 12 seconds = 504 seconds
Correct Option: C
Required time = LCM of 6, 7, 8, 9 and 12 seconds = 504 seconds
 The greatest number of four digits which when divided by 3, 5, 7, 9 leave remainders 1, 3, 5, 7 respectively is :

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The difference between divisor and the corresponding remainder is equal.
LCM of 3, 5, 7 and 9 = 315
Largest 4digit number = 9999
∴ Number divisible by 315 = 9999 – 234 = 9765Correct Option: A
The difference between divisor and the corresponding remainder is equal.
LCM of 3, 5, 7 and 9 = 315
Largest 4digit number = 9999
∴ Number divisible by 315 = 9999 – 234 = 9765
Required number = 9765 – 2 = 9763
 Three bells ring simultaneously at 11a.m. They ring at regular intervals of 20 minutes, 30 minutes, 40 minutes respectively. The time when all the three ring together next is

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LCM of 20, 30 and 40 minutes = 120 minutes
Hence, the bells will toll together again after 2 hours i.e. at 1 p.m.Correct Option: B
LCM of 20, 30 and 40 minutes = 120 minutes
Hence, the bells will toll together again after 2 hours i.e. at 1 p.m.
Required time = 1 p.m.
 Four bells ring at the intervals of 5, 6, 8 and 9 seconds. All the bells ring simultaneously at some time. They will again ring simultaneously after

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The LCM of 5, 6, 8 and 9 = 360 seconds = 6 minutes
Correct Option: A
The LCM of 5, 6, 8 and 9 = 360 seconds = 6 minutes
Hence , They will again ring simultaneously after 6 minutes .