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A certain high school with a total enrollment of 900 [#permalink]
15 Jul 2004, 20:37
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15. A certain high school with a total enrollment of 900 students held a science fair for three days last week. How many of the students enrolled in the high school attended the science fair on all three days?
(1) Of the students enrolled in the school, 30 percent attended the science fair on two or more days.
(2) Of the students enrolled in the school, 10 percent of those that attended the science fair on at least one day attended on all three days
B is taking a percentage of a percentage. Look at the "of" word and you'll see it. "10% of those who attended at least one day".
So if 200 people went on one day, and 70 people went for two days, and 30 people went for all three days, then together that makes 300 people, and 10% of that is the number that went for three full days, 30.
or, if you like algebra, then say that x people went for one day, y people went for two days, and z people went for three days, so .1(x+y+z)=z