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numb properties from kaplan

by wawatan » Mon Jun 23, 2008 5:47 pm
i just took a diagnostic test so this question came up

If z is an integer multiple of both 6 and 10 then it must also be an integer multiple of

12
15
20
40
60

i thought the answer is 60
please explain what is wrong with 60.... thanks
but the OA is 15 :cry:
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by pranavc » Mon Jun 23, 2008 6:12 pm
I can't for the life of me figure out how the answer would NOT be 60. Any input would be highly appreciated. Thanks in advance.
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by Ian Stewart » Mon Jun 23, 2008 6:44 pm
If a number is an integer multiple of 6 and 10, the most you can say is that it's a multiple of the LCM of 6 and 10, i.e. of 30. If z must be a multiple of 30, z must be a multiple of 15, and B is the correct answer.

If you are wondering why 60 is not the correct answer, note that z could be 30 here. 30 is a multiple of both 6 and 10, but is not a multiple of 60.
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