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Counting method, theory of nb

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by kvcpk » Thu Jun 17, 2010 7:44 am
francoisph wrote:How many different positive integers exist between 106 and 107, the sum of whose digits is equal to 2?
Are you sure about the question?
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by amising6 » Thu Jun 17, 2010 7:49 am
How many different positive integers exist between 106 and 107, the sum of whose digits is equal to 2?
something missing range is wrong i guess
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by francoisph » Thu Jun 17, 2010 2:45 pm
How many different positive integers exist between 106 and 107, the sum of whose digits is equal to 2?

A. 6
B. 7
C. 5
D. 8
E. 18

The correct choice is (B) and the correct answer is 7.

The answer is 7 could you explain please?
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by sk818020 » Thu Jun 17, 2010 3:13 pm
I agree with the posters before me. I'm rather certain that no integer can exist that is defined as x, and 106<x<107. Integers are whole numbers.

Are you sure its not,


How many positive integers exist between 10^6 and 10^7 whose sum is equal to 2?

Thanks,

Jared
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by sk818020 » Thu Jun 17, 2010 3:23 pm
Are you sure its not,

How many positive integers exist between 10^6 and 10^7 whose sum is equal to 2?

If so then 7 would make sense because,

Were thinking of all the numbers that could add to 2 between 1,000,000 and 9,999,999. The only numbers that would add to to are those with two ones and the rest zeros and numbers with one two and the rest zeros.

You could do the math;

Combinations of 1000001, where the first one must stay and place is; 6!/(5!*1!)=6

And there would only be one number with a 2 at the beginning and rest are zeros; 2,000,000.

If you dont want to do the math just write it out.

1,000,001
1,000,010
1,000,100
1,001,000
1,010,000
1,100,000
2,000,000

Thanks,

Jared
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