Question

By what prime number may 159 be divided ,so that the reminder is 5

Answer 1

it should be divided by 7

Answer 2

To find the prime number that should divide 159 (since 159 is prime, it won't be perfectly divisible):
The greatest square number near to 159 is 169.
Square root of 169 is 13.
Hence prime numbers less than 13 are 11,7,5,3,2
159/11--Remainder = 5
159/7--- Remainder = 5 
Hence '11' and '7' are the prime numbers.
Hope it helps.