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How many integers can be formed using the prime numbers below 9 that lies between 5000 to 9000, where 1st two digits are same as next two digits.

Option: 1

15


Option: 2

18


Option: 3

16


Option: 4

10


Answers (1)

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To find the number of integers that can be formed using the prime numbers below 9 (2, 3, 5, and 7) where the first two digits are the same as the next two digits to form a 4-digit number between 5000 and 9000, we can consider the following cases:

Case 1: The first two digits are 22
In this case, we only have one choice for the first two digits (22). For the next two digits, we have 4 choices (2, 3, 5, and 7). So, the total number of integers in this case is:
1\times 4= 4
 

Case 3: The first two digits are 55In this case, we only have one choice for the first two digits (55). For the next two digits, we have 4 choices (2, 3, 7 since 5 is already used). So, the total number of integers in this case is:
1\times 4= 4

Case 4: The first two digits are 77
In this case, we only have one choice for the first two digits (77). For the next two digits, we have 4 choices (2, 3, 5 since 7 is already used). So, the total number of integers in this case is:
1\times 4= 4

Adding up the four cases, we get:
4+4+4+4= 16

Therefore, the number of integers that can be formed using the prime numbers below 9 (2, 3, 5, and 7) where the first two digits are the same as the next two digits to form a 4-digit number between 5000 and 9000 is 16.

 

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Rishi

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