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3-digit numerals

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by harsh.champ » Tue Feb 09, 2010 4:55 am
How many 3-digit numerals begin with a digit that represents a prime and end with a digit that represents a prime number?

(A)16
(B)80
(C)160
(D)180
(E)240

The OA is C.
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Source: — Problem Solving |

by shashank.ism » Tue Feb 09, 2010 4:58 am
harsh.champ wrote:How many 3-digit numerals begin with a digit that represents a prime and end with a digit that represents a prime number?

(A)16
(B)80
(C)160
(D)180
(E)240

The OA is C.
The first digit can be 2, 3, 5, or 7 (4 choices) The second digit can be 0, 1, 2, 3, 4, 5, 6, 7, 8, or 9 (10 choices)
The third digit can be 2, 3, 5, or 7 (4 choices) 4 * 4 * 10 = 160
Ans is C
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by ajith » Tue Feb 09, 2010 6:55 am
harsh.champ wrote:How many 3-digit numerals begin with a digit that represents a prime and end with a digit that represents a prime number?

(A)16
(B)80
(C)160
(D)180
(E)240

The OA is C.
first digit can be 2,3,5,7 =4 possibilities
Last digit can be 2,3,5,7 =4 possibilities
Middle digit can be 0-9 =10 possibilities

total = 4*4*10 = 160
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