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One day, Lee decides to write down the numbers    1.....999

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

 

 

i think this means it's asking for the number of 7 digits from 1....999

 Jan 29, 2020
 #1
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The digit 7 appears 297 times, so the probability is 297/2889 = 11/107.

 Jan 29, 2020
 #2
avatar+107414 
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How do you know it appears 297 times?   You should explain your answer.

Melody  Jan 29, 2020
edited by Melody  Jan 29, 2020
 #3
avatar+20216 
+2

Not sure about that answer   

 

I count up in my head   300    7's    

   out of  2889 digits  (see previous answer)

 

300/2889 =100/963

 Jan 29, 2020
 #4
avatar+107414 
+1

 

 

One day, Lee decides to write down the numbers    1.....999

How many times does 7 appear.

 

Lets see.

 

Units

Each decade 7 apears once.  100 decades so that is 100 times

 

Place value 10

Each century seven appears 10 times,  10 centuries so that is  100 sevens

 

Place value 100

Each millenium seven appears 100 times

 

So I get 300 times.  You got 297.  Who is wrong?

-------------------

 

If 7 appears 300 times it stands to reason that so do 1,2,3,4,5,6,8, and 9 do too.

How about 0

units   first decade not at all so that is 99 times

tens    first century not at all so that is 90 times

hundreds first milenium not at all so that is 0 times

So zero appears 189 times I think

 

300*9+189=2889 digits altogether.

 

so I get      300/2889   Same as EP.

I could easily have miscounted.

 Jan 29, 2020
edited by Melody  Jan 29, 2020
 #5
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I believe that answer is correct... I got the same thing

Guest Jan 30, 2020
 #6
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Quick follow-up question, do you know what the sum of all the digits are?

Guest Jan 30, 2020
 #7
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Sum of the digits from 1 to 999 inclusive =13,500

Guest Jan 30, 2020

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