Answer:
N:10
Step-by-step explanation:
Answer: 
Step-by-step explanation:
You have the equation
.
Then, to solve for the variable
from the equation you need:
Make the subtraction of the right side of the equation:
(As the denominators are 1 and
, the least common denominator is
)

Multiply
to both sides:

Add
to both sides:

And finally divide both sides by
:

A counter-example could be
There are more than 3 marbles in the bag, and the other ones are red.
Hope this helps!