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Manager
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Re: M01 #10 [#permalink] New post 04 Nov 2011, 19:56
Answer is 300, D.

Units Digit: 007, 017....097 = 10
Tens Digit: 070, 071...079 = 10

So there are 10 + 10 = 20 instances of 7 in each hundred numbers. So in 1000 numbers, there are 10 x 100 numbers = 20 x 10 = 200 instances of 7 in 1000 for units and tens digits.

Hundreds digit: 700, 701...799 = 100 instances of 7 for the hundreds digit.

So from 1-1000, there are 200 + 100 = 300 instances of 7.

Hope that helps!!!
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Re: M01 #10 [#permalink] New post 18 Nov 2011, 02:42
single digit number 7 will appear once.
2 digit number 7 will appear = 9 time at unit digit and 10 times at 10th digit. = 19 times
3 digit number 7 will appear = 100 times for 100th digit + 90 times fo 10th times +90 times for 90 times for unit digit = total 280

so total number of times 7 appears between 1 to 1000 = 280+19+1 = 300
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Re: M01 #10 [#permalink] New post 14 Jan 2012, 21:57
IMO - D
Best way to solve this .

100's place = 1x10x10 = 100
10's place = 10x1x10 = 100
1's place = 10x10x1 = 100
Re: M01 #10   [#permalink] 14 Jan 2012, 21:57
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