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# How many times will the digit 7 be written when listing the

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VP
Joined: 05 Jul 2008
Posts: 1403

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How many times will the digit 7 be written when listing the [#permalink]

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10 Oct 2008, 17:23
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

How many times will the digit 7 be written when listing the integers from 1 to 1000?

* 110
* 111
* 271
* 300
* 304

I took a long long time to solve this and finally threw a hail mary pass. I want to look at different or easy approaches to solve this.

Thanks

Kudos [?]: 423 [0], given: 1

Senior Manager
Joined: 21 Apr 2008
Posts: 269

Kudos [?]: 161 [0], given: 0

Location: Motortown
Re: Number 7 [#permalink]

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10 Oct 2008, 18:01
D - 300

1to100 : 20 times
101to200 : 20 times
.
.
.
.
901to1000:20times
Total = 200
plus
700's = 100
= 300

PS: If someone could come up with a better implementation/answer, I would appreciate it too...

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Manager
Joined: 09 Oct 2008
Posts: 93

Kudos [?]: 24 [0], given: 0

Re: Number 7 [#permalink]

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10 Oct 2008, 18:20
please remaimber this thing:

how many time 7 or 8 or 5 comes between 1 to 1000

I think each number(except 0) will come 20 times from1 to 100 ".................1

so in 1 to 1000 mulitply this by 10:20 *10 =200

now each number hase its own series for 3 digitnumber :1xx,2xx,9xx

again each number will come 100 times.

so total 100 +200 = 300
* This thing can certainly save your 2min.in exam

Someone please confirm/correct this:

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VP
Joined: 30 Jun 2008
Posts: 1033

Kudos [?]: 688 [0], given: 1

Re: Number 7 [#permalink]

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10 Oct 2008, 20:08
icandy wrote:
How many times will the digit 7 be written when listing the integers from 1 to 1000?

* 110
* 111
* 271
* 300
* 304

I took a long long time to solve this and finally threw a hail mary pass. I want to look at different or easy approaches to solve this.

Thanks

Unfortunately, we don't have any formulaic approach here. Go by the Unit, tens and hundreds approach so that you don't miss any number.

The number 7 at units place appears once in every 10 digits. So in the first 100 numbers, 7 appears 10 times. We have 10 100s here (100*10= 1000) so we have 7 at units place in 10*10 =100

Next tens place. Again we have 7 appearing 10 times in tens place in the first 100. We have 10 100s(100*10= 1000) here. So 7 at tens place = 10*10 = 100

Next hundreds place. In the first 100 numbers, We have 7 appearing 100 times in hundreds place (from 700 to 799) so that makes another 100.

Add up the three 100s we get 300
_________________

"You have to find it. No one else can find it for you." - Bjorn Borg

Kudos [?]: 688 [0], given: 1

Re: Number 7   [#permalink] 10 Oct 2008, 20:08
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# How many times will the digit 7 be written when listing the

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