The whole number one is equal to what parts out of two?
Here is one whole circle. And our one whole circle is shaded. Here is our second circle. Our second circle is made up of two pieces. But we know that these two circles are equal. They both have the same amount of shaded space.
One whole circle, one whole is equal to two out of two, because the fraction form of the number one has the same numerator as the denominator. The number one written as a fraction out of two is equal to two over two.