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How many integers between 2,000 and 3,999 have a units digit that is a

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How many integers between 2,000 and 3,999 have a units digit that is a  [#permalink]

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New post 21 Dec 2018, 02:57
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A
B
C
D
E

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  35% (medium)

Question Stats:

70% (01:39) correct 30% (01:45) wrong based on 91 sessions

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Re: How many integers between 2,000 and 3,999 have a units digit that is a  [#permalink]

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New post 21 Dec 2018, 03:27
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Bunuel wrote:
How many integers between 2,000 and 3,999 have a units digit that is a prime number?

A. 200
B. 400
C. 798
D. 800
E. 801


Per 100, a prime number appears 10 times in the units digit. There are 4 prime numbers i.e. 2,3,5,7. Hence, per 100, the units digit that is a prime number occurs 40 times.
There are (3999-2000)/100=19.99 hundreds, or for approximation sake, 20 hundreds. Therefore, the total number of integers between 2,000 and 3,999 are 40*20=800.
IMO, Option D.
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Re: How many integers between 2,000 and 3,999 have a units digit that is a  [#permalink]

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New post 21 Dec 2018, 04:00
Bunuel wrote:
How many integers between 2,000 and 3,999 have a units digit that is a prime number?

A. 200
B. 400
C. 798
D. 800
E. 801



integers which can have units digit as a prime are 2,3,5,7 so only integers with these 4 digits can suffice ..

so in a range of 100 numbers say 2000- 2100 we have : 4* 10 = 40 such integers

and total integers given : 3999-2000= 1999
so we can say 1999*4/100 = 799.6 ~ 800 IMO D
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How many integers between 2,000 and 3,999 have a units digit that is a  [#permalink]

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New post 26 Dec 2018, 13:01
Bunuel wrote:
How many integers between 2,000 and 3,999 have a units digit that is a prime number?

A. 200
B. 400
C. 798
D. 800
E. 801


Between 2000 - 2999
1*10*10*4 =400 ( units digit has 4 options ,2,3,5,7. Tens digit has 10 options from 0 to 9,Same with Hundred Digit, and thousand digit has only one option, i.e. 2 )

Between 3000 -3999
1*10*10*4 =400( units digit has 4 options ,2,3,5,7. Tens digit has 10 options from 0 to 9,Same with Hundred Digit, and thousand digit has only one option, i.e. 3 )

So 400+400=800
Answer -> D
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How many integers between 2,000 and 3,999 have a units digit that is a   [#permalink] 26 Dec 2018, 13:01
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