How many prime numbers between 50 to 100?  Answers:
A) 11	B) 10	C) 15	D) 14	E) 12
primes are of the form 6n+1 or 6n-1   Put n=9   6n+1=6*9+1= 
<gadget id="calculator">6*9+1</gadget>
<output>55</output>
55 where 55 is not prime   for n=9   6n-1=6*9-1= 
<gadget id="calculator">6*9-1</gadget>
<output>53</output>
53   for n=10 , 6n-1= 59 and 61   for n=11 , ==&gt; 67   for n =12 ==&gt; 73 and 71   for n =13 ==&gt; 79   for n =14 ==&gt; 83   for n=15 ==&gt; 89   for n =16 ==&gt; 97   therefore total number of prime numbers = 10   Ans - 10
<result>B</result>
How many prime numbers between 50 to 100?