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Probability

Expert replies
by evansbd » Tue Jul 22, 2008 10:59 am
In a basketball contest, players must make 10 free throws. Assuming a player has 90% chance of making each of his shots, how likely is it that he will make all of his first 10 shots?

a) 10%
b) 25%
c) 35%
d) 45%
c) 55%


How many randomly assembled people do u need to have a better than 50% prob. that at least 1 of them was born in a leap year?

a) 2
b) 3
c) 4
d) 5
c) 7


I generally know how to do each problem, but I'm not sure if I could do each without a calculator very quickly.
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Source: — Problem Solving |

by egybs » Tue Jul 22, 2008 11:13 am
We're looking for .9^10

There may be some really easy shortcut... but it's actually pretty quick to roughly estimate it out.

Just start with 1, and remove 10%... then remove 10% from that number.. then remove around %10 from that number... and so on... do this a total of 10 times. This shouldn't take more than 60 seconds to do and gets you really close to the answer.

.9
.81
.73
.66
.6
.54
.5
.45
.4
.36

So, C.
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