Probability is always in a fraction /decimal form. The meaning of probability is :' what are the chances of something happening?' . So in this case, they are asking what are the chances of the arrow landing on a blue tile. So you need to know how many possible tiles are there to land on. So since the circle is split into 8 parts, there is a total of 8 different tiles. Out of the 8 tiles, there are 2 blue tiles. So the fraction is total chances of blue colour / total possible tiles = 2/8= 1/4. This is the probability.