Wednesday, July 31, 2013

number, LCM and divisibility -- IPM STD V

Find the number of integers between 200 and 600 divisible by 2,3 and 7?


Answer:

if a number is divisible by 2,3 and 7, it must be divisible by the LCM of the three numbers.
LCM of 2, 3, and 7 is 42.

42 have 4 multiples in 200 (i.e. 200/ 42 = 4 32/42)
And 42 have 14 multiples in 600 (i.e. 600/42 = 14 12/42)
So, number of integers between 200 and 600 that is divisible by 42 = 14 – 4 = 10.
Answer.

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