Gmater-1 Posted December 26, 2007 Share Posted December 26, 2007 how to solve it a faster way, I was unable to do it in less than 2 mins, coz i had to list down all the prime number :) OA is D Quote Link to comment Share on other sites More sharing options...
manish8109 Posted December 26, 2007 Share Posted December 26, 2007 All prime numbers are odd except 2 so, odd+odd=even even+odd=odd so, check for 19 it is 2+17=19(both 2 & 17 are prime) check for 45 it is 2+43=45 (both 2& 43 are prime) check for 68 as it is even so both prime number if applicable should be odd 61+7=68 (both 61 & 7 are prime) check for 79 as it is an odd number it means one of the prime number should be even i.e. 2+77=79 but 77 is not prime so Ans is 79-----(D) Check for 88 (even) means both prime number should be odd i.e. 83+5=88(both 5 & 83 are prime) Ans is (D) Quote Link to comment Share on other sites More sharing options...
Gmater-1 Posted December 27, 2007 Author Share Posted December 27, 2007 Hey Manish!! Nice to see you back on forum and that too replying to my posts :) So Manish I guess you would have completed you MBA?? Quote Link to comment Share on other sites More sharing options...
krusta80 Posted December 27, 2007 Share Posted December 27, 2007 how to solve it a faster way, I was unable to do it in less than 2 mins, coz i had to list down all the prime number :) OA is D Start with the odd numbers, because you know that an odd sum of two integers has to have one even integer and one odd integer. Since 2 is the only even prime, it HAS to be one of the numbers for the odd choices. Therefore, subtract 2 from each odd choice, and whichever result is not prime is your answer. A. 19 - 2 = 17 PRIME B. 43 - 2 = 43 PRIME D. 79 - 2 = 77 NOT PRIME D is the answer. Quote Link to comment Share on other sites More sharing options...
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