In a bag there are 13 red candies, 13 green candies 13 yellow candies and 13 blue candies. If I pick 1 candy from the bag what is the probability that it will not be blue?

How many blue candles ?
How many in total?

So it's then

To calculate the probability of a certain event (picking a non-blue candy in this case), you simply take the number possible positive outcomes (in this case, the total number of non-blue candies in the bag) divided by the total number of outcomes (in this case, the total number of candies in the bag, regardless of color).

So how many non-blue candies are in the bag? How many candies total are in the bag? What's the first answer divided by the second answer?

Right, except that if you read carefully, you'll see it asked about the probability that it will NOT be blue. So it's actually non-blue/total.