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SETS & FACTORS

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wingsoffire Just gettin' started!
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SETS & FACTORS Post Mon Oct 03, 2011 6:10 am
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    How many positive integers less than 1000 are multiples of 5 but NOT of 4 or 7?

    a)114
    b)121
    c)122
    d)129
    e)136







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    rajanjindal27 Just gettin' started! Default Avatar
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    Post Thu Oct 06, 2011 12:10 am
    129

    razorback Just gettin' started! Default Avatar
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    Post Fri Oct 07, 2011 5:46 pm
    129.

    20 multiples of 5 in each 100 number set (5,10,15...90,95,100)
    = 20(10)

    subtract 5 from each set that are multiples of 4 (20,40,60,80,100) <-- takes care of 1000 since its "less than 1000"

    so now its 15(10).

    subtract 21 for all the multiples of 7 (manually crunched it, didn't double count the multiples of 4 already subtracted).

    =150 - 21 = 129

    Took about 3 minutes with the manual number crunching of multiples of 7 that didnt double dip the fours.

    Thanked by: wingsoffire

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