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Question

A positive integer is said to be prime if it is not divisible by any positive integer other than itself and one. Let K be a prime number strictly greater than 5. When K2+19 is divided by 12, the remainder will be:

The correct answer is

8

Let K be a prime number greater than 5. Then K can be written in the form 6n+1 or 6n+5 for some integer n. Case 1: K = 6n+1 K2 + 19 = (6n+1)2 + 19 = 36n2 + 12n + 1 + 19 = 36n2 + 12n + 20 When divided by 12, the remainder is 8. Case 2: K = 6n+5 K2 + 19 = (6n+5)2 + 19 = 36n2 + 60n + 25 + 19 = 36n2 + 60n + 44 When divided by 12, the remainder is 8. In both cases, the remainder is 8.

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Important Questions from Number System

  1. Consider the following statements :

    1. (25)! + 1 is divisible by 26

    2. (6)! + 1 is divisible by 7

    Which of the above statements is/are correct ?

  2. If the sum S is divided by 8, what is the remainder ?  

  3. If the sum S is divided by 60, what is the remainder ?

  4. Find the sum of squares of the greatest value and the smallest value of K in the number so that the number 45082K is divisible by 3.

  5. How many composite numbers are there from 53 to 97 ?

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