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science book

by hakyology » Tue Aug 05, 2008 9:55 am
Of the science books in a certain supply room, 50 are on botany, 65 are on zoology, 90 are on physics. 50 are on geology, 110 are on chemistry. If science books are removed randomly from the supply room, how many must be removed to ensure that 80 of the books removed are on the same science?

a)81
b)159
c)166
d)285
e)324


the answer is 324.

please explain .thanks.
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by parallel_chase » Tue Aug 05, 2008 10:11 am
You want to remove 80 books of the same science.

Lets take the worst case scenario.

remove 79 from botany = we only have 50
remove 79 from zoology= we only have 65
remove 79 from physics =79
remove 79 from geology= we only have 50
remove 79 from chemistry= 79

50+65+79+50+79= 323

Now we just have to pick 1 more book to make sure we at least have 80 of same science

323+1=324

Let me know if you have any doubts.
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