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# hELp iS nEeDed qUiCk!

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One day, River writes down the numbers 1,2,...,999

River chooses one of the digits written down at random. What is the probability that River chooses a 7?

Thank you and please provide an explanation!

:)

Apr 30, 2020

### 5+0 Answers

#1
+657
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OK Here is my best shot :D

There are 280 numbers contain the digit 7 between 0 and 999.

So 280/999

Here to help

:D

Apr 30, 2020
#2
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If repeated digits are counted, such as 77, 777.....etc, then there are 300 sevens between 1 and 999.

If repeated digits are NOT counted, then there are 271 sevens between 1 and 999.

Then, the probability is either   300 / 999  or  271 / 999.

Apr 30, 2020
#3
+111329
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I get a slightly different result

The number of digits written down =

9  + 2(99 - 10 + 1)  + 3(999 - 100 + 1)  =

9 + 2 ( 90)  + 3(900)  =

2889

The number of  7's  that are written down  =

10*10  + 10(10)  + 100  =   300

So.....the probability  of  selecting a "7"  =   300 / 2889  = 100/963

Apr 30, 2020
#4
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Ahhhh wait CHphill I'm doing an AOPs online course and I remember getting this question right in fact you are right the answer is indeed 100/963

Great work as usalll!

Here to help

:D

LuckyDucky  Apr 30, 2020
#5
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yay that's right! thanks CPhill! :)

lokiisnotdead  Apr 30, 2020