The triangles vary in size in order to make the solution clearly about quantity, not "total mass".
Adjacent-numbered pages: BP1203 BP1204 BP1205 BP1206 BP1207  *  BP1209 BP1210 BP1211 BP1212 BP1213
stub, precise, spectrum, dual, handed, leftright, traditional
Aaron David Fairbanks
BP1217 has the same solution but rotated a quarter-turn counter-clockwise.
Adjacent-numbered pages: BP1209 BP1210 BP1211 BP1212 BP1213  *  BP1215 BP1216 BP1217 BP1218 BP1219
stub, dual, handed, leftright, traditional
BP1214 has the same solution but rotated a quarter-turn clockwise.
Adjacent-numbered pages: BP1212 BP1213 BP1214 BP1215 BP1216  *  BP1218 BP1219 BP1220 BP1221 BP1222
stub, dual, handed, updown, traditional