Product of units the given numbers = `(6 xx 7 xx 9 xx 2) = 756`
  `:.` unit digit in the given product is `6`.

sol.Clearly ,unit digit in `3^4` is 1.
      
     :. unit digit in `3^64` is 1.
      
     :. unit digit in `3^67` is 7. [unit digit in `1 xx 3 xx 3 xx 3` is 7]
       
      clearly unit digit in every power of 6 is 6.
       
      :.unit digit in `6^39` is 6.
       
       clearly unit digit in `7^4` is 1.
     
       :. unit digit in `7^72`is 1.
       
       :. unit digit in `7^53`is 7. [unit digit in `1 xx 7` is 7]
        
       :.unit digit in given product =unit digit in`(7 xx 6 xx 7) = 4`

Sol.(i) ,14>√191.
prime numbers less than 14 are 2.3,5,7,11,13.
191 is not divisible by any of them .
So 191 is a prime number.

(ii) Clearly,16>√241.
 prime numbers less than 16 are 2,3,5,7,11,13.
  241 is not divisible by any of them. 
:.241 is a prime number.
 (iii) Clearly,19>√337.
 prime numbers less than 19 are 2,3,5,7,11,13,17.
337 is not disivible by any of them.
:. 337 is a prime number.
(iv)Clearly,20>√391.
 prime number less than 20 are 2,3,5,7,11,13,17,19.
We find than 391 is divisible by 17.
:. 391 is not prime.

Sol.Clearly,the unit,s digit of 913o525 is 5,which is not divisible by 2.
So,9130525 is not disivible by 2.
Each of the numbers has a unit digit disivible by 2.
So, each one other than 9130525 is disivible by 2.

Sol.(i) Sum of digit in 541326 is 21,which is divisible by 3.
So,541326 is divisible by 3.
  (ii) Sum of digits in 5967013 is 31,which is not divisible by 3.
  Hence,5967013 is not divisible  by 3.