Which is a prime number? Will medal and fan

A.
39

B.
49

C.
81

D.
89

Question

Which is a prime number?	 Will medal and fan
 
 A.
39
 
 B.
49
 
 C.
81
 
 D.
89

anonymous · Answer

wow....um...this is hard

anonymous · Answer

I almost got the answer

anonymous · Answer

but solomonzelman has it he knows...lol

solomonzelman · Answer

prime number is a number that can be divided by itself and by 1 only.
(1 and 0 are not included)

for example:
2, 3, 5, 7, 11, 17 etc...

anonymous · Answer

its either 39 or 89 let me check

solomonzelman · Answer

(and there are I think 6 proves for why there is an infinity of prime numbers. That they don't end at a certain point)

anonymous · Answer

the answer is 89

solomonzelman · Answer

39 is divisible by 3 and that you can tell.
sqrt(49) is 7^2, you should remember those:)

sqrt(81) is 9^2. Another way to tell that 81 is divisible by 3 is to add the digits and to see if the sum is divisible by 3 or not. 81 -> 8+1 -> 9.
Yup, 9 (the sum of digits) is divisible by 3, and therefore 81 is also).

89 is prime.

anonymous · Answer

Yah I was right lol.  Prime and composite numbers are pretty easy to me, but I still stink at math =P

solomonzelman · Answer

I am not any good at math either, don't worry about it.

anonymous · Answer

Lol cool! @SolomonZelman