The Russian abacus (tchoty) is held so that counters move crosswise. It has no crossbar, and all counters in one row have the same value. Most rods have ten counters. An occasional row has fewer, to ...

This can be solved by partitioning one of the numbers. Here are two tens frames showing 8 orange counters. Here are 4 yellow counters which are going to be added to the 8 orange counters.

The abacus is a computing device on which arithmetic calculations are performed by sliding counters (beads, pebbles, or flat discs) along rods, wires or lines. The instrument may have originated in ...