Shade 8 cells; divide into 4 equal groups.
Shade 15 cells; divide into 3 equal groups.
Shade 16 cells; divide into 3 equal groups. Remainder =1
etc.
Shade 8 cells; divide into 4 equal groups.
Shade 15 cells; divide into 3 equal groups.
Shade 16 cells; divide into 3 equal groups. Remainder =1
etc.