If darts are thrown at this board, what is the probability it will land in sector 1 or sector 3?

Think about it, section 2 is 2pi/3 which makes section 1 pi/3, and it's the same for 4 = 2pi/3 and 3 = pi/3. So you have a total of 2pi/3 for section 1 and 3... since there's a total of 6pi/3 or just 2 pi in a circle, so with that case how much is 2pi/3 out of 6pi/3... it's 1/3rd.