the sum of pie wheel
The two sliders of the left top most corner represent the fraction quantity of the left most pie wheel, having m as its numerator and n as its denominator. Whereas the two sliders of the middle top represent the fraction quantity of the middle pie wheel, having b as its numerator and a as its denominator. The pie wheel of the right most corner represents the sum of the fractions of the other two pie wheels. What is so convenient about this pie wheel is that the outcome is reduced to its smallest fraction. Thanks to a special GCD feature from Geogebra.