A box contains tiles, numbered 1, 2, 3,..., 49, 50. Only tiles which are marked with a number congruent to 2 mod 8 are blue. One tile is chosen randomly from the box. What is the probability that the tile is blue?

The following numbers are congruent to 2 mod 8:

2 , 10 , 18 , 26 , 34 , 42 , 50 == 7 numbers out of 50

Therefore, the probability is: 7 / 50