Is the positive integer y a prime number?

Target question: Is y a prime number?

Given: y is a positive integer

Statement 1: 80 < y < 95
This statement doesn't FEEL sufficient, so I'll TEST some values.
There are several values of y that satisfy statement 1. Here are two:
Case a: y = 81, in which case y is NOT prime
Case b: y = 83, in which case y IS prime
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Aside: For more on this idea of plugging in values when a statement doesn't feel sufficient, you can read my article: https://www.gmatprepnow.com/articles/dat ... lug-values

Statement 2: y = 3x + 1, where x is a positive integer
There are several values of y that satisfy statement 2. Here are two:
Case a: y = (3)(1) + 1 = 4, in which case y is NOT prime
Case b: y = (3)(2) + 1 = 7, in which case y IS prime
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined
Let's list ALL possible values of y.
y = (3)(27) + 1 = 82 (82 is NOT prime)
y = (3)(28) + 1 = 85 (85 is NOT prime)
y = (3)(29) + 1 = 88 (88 is NOT prime)
y = (3)(30) + 1 = 91 (91 is NOT prime)(91 = 13 times 7)
y = (3)(31) + 1 = 94 (94 is NOT prime)
So, we can conclude that y is NOT prime
Since we can answer the target question with certainty, the combined statements are SUFFICIENT

Answer = C

Cheers,
Brent