Which is a counterexample that disproves the conjecture?

If n is a positive integer, then 2n – 1 is a prime number.

A.
n = 6

B.
n = 5

C.
n = 3

D.
n = 2

Question

Which is a counterexample that disproves the conjecture?


       If n is a positive integer, then 2n – 1 is a prime number.
 
 A.
n = 6
 
 B.
n = 5
 
 C.
n = 3
 
 D.
n = 2

thefluffmuncher · Answer

@rishi_84

ganeshie8 · Answer

prime numbers wud be very boring if that conjecture was true lol

ganeshie8 · Answer

plugin each option into the given expression and see which one does not give u a prime number...

thefluffmuncher · Answer

a is eliminated

thefluffmuncher · Answer

it's b right

ganeshie8 · Answer

lets test first option :
 A.
n = 6

2n - 1 =  2(6)  - 1 = 12 - 1 = 11
is a prime number, so its not a counter example. Yes eliminate this.

ganeshie8 · Answer

You got it ! B is a counter example cuz 2(5) - 1 = 10 - 1 = 9 is NOT a prime number

thefluffmuncher · Answer

yay im like half asleep and i got it right woohoo!

ganeshie8 · Answer

good job :)

anonymous · Answer

bro b will be option because 2*5-1 = 9 is not a prime