Assemble A, B, and C Units
1. Use a pencil to mark an X on the wrong side of each red print 10" square (Diagram 1). (To prevent fabric from stretching as you draw lines, place 220-grit sandpaper under each square.)
2. Layer a marked red print square atop a blue print 10" square. Sew together, stitching 1⁄4" on each side of drawn lines (Diagram 2).
3. Referring to Diagram 3, cut joined squares apart through horizontal and vertical centers to make four 5" squares. Then cut squares apart on drawn lines to make eight triangles. Press one triangle open to make a Unit A (Diagram 4). Press open remaining triangles to make eight A units total. Using the 45° diagonal line on an acrylic ruler, trim each unit to 4-1⁄2" square including seam allowances.
4. Repeat steps 2 and 3 to make 40 A units total.
5. Referring to Step 1, draw an X on the wrong side of each yellow print 10" square.
6. Repeat steps 2 and 3 using the marked yellow print squares and the black print 10" squares to make 40 B units (Diagram 5).
7. Repeat steps 2 and 3 using remaining marked red print squares and remaining black print 10" squares to make 40 C units (Diagram 5).