There are 5 blue rectangles out of 10 total. This forms the fraction 5/10 and that reduces to 1/2 after dividing both parts by 5. Therefore, the fractions 5/10 and 1/2 are the same. Notice that exactly half of the entire figure is shaded blue.
Use long division or your calculator to find that 1/2 = 0.5 which converts to 50% when you move the decimal point 2 spots to the right.
