Important number system math question and answer for bank,bcs and others compititive exams part-1
Important number system math question and answe r for bank,bcs and others compititive exams Prime number related question and Answer Question: Which of the following is a prime number A. 19 B. 20 C. 21 D. 22 Answer: A Solution: Clearly,19 is a prime number. Question: Which is not a prime number? A. 13 B. 19 C. 21 D. 17 Answer: C Solution: 21=3*7 is not a prime number because 21 is a composite number. Question: which of the following is a prime number? A. 143 B. 289 C. 117 D. 359 Answer: D Solution: Clearly,143=13*11 so, 143 is not prime. 289=17*17 so ,289 is not a prime number. 359 is not exactly divisible by any of them. so 359 is a prime number. Question: The smallest value of natural number n, for which 2n+1 is not a prime number, is A. 3 B. 4 C. 5 D. None Answer B Solution: Putting n=1,2,3,4 respectively in (2n+1) we get: (2*1+1)=1, (2*2+1)=5, (2*3+1)=7 and (2*4+1)= 9, Where 3,5,7 are prime numbers. But 9 is not a prime number. The smallest value of n f...