prime number issues

51,53,57,59,61

as they are divisible by them only. no need to memorise

51 & 57 are divisible by 3.
use the strings "prime numbers 1-100" in Google.
Ans to ur Q 53 59 61 67 71

sorry i hvt checked 51 n 57

Why would you want to memorize them? sounds like a lot of effort for a little reward - it is better to know the rules of divisibility for the numbers from 2-11 and check divisibility if you are looking for primes - less room for error and almost as fast if you get good at divisibility rules which will help you on every area of the test.

because you have 2 minutes to find the result

wasted time I think if you should count on various numbers (div by itself and 1 )

@ francoisph
Is it possible to post the particular Q where you had to use the knowledge of prime nos. ? Thnaks.

This might help

1.write down all the odd nos from the no given (In ur example 50)

I,e 51,53,55,57,59,61,6365,67,69,71

2.cancle the nos that are divisible,ex:51--sum is 6 ,so div by 3 ,cancle it ,lly u can eliminate the remaining

so 53,59,61, 67 ,71..

(u should know the divisibility rules though)