Abacus Practice Online: Sums by Rule, on the Abacus or in Your Head

Which kind of sums?

Direct sums need no friends: the beads you need are free. Small friends are the friends of 5: when there are not enough bottom beads, +4 becomes +5 −1. Big friends are the friends of 10: +9 becomes −1 +10 on the next rod. Mixed sums use any rule, and Columns add and take away three to five numbers in a row, as on an abacus worksheet.

On the abacus or in your head

On the abacus, the first number is already set: move the dice to the answer, one number at a time, and the clock starts with your first move. Stuck? “Show me” rings the die to move next, but then that sum does not count as right first time. In your head, the abacus is covered: picture the dice moving and type the total, the way abacus learners do mental math.

Daily gives everyone the same ten mixed sums each day; Progress opens your stats, where the rules chart shows which kind of sum needs more practice. New to the abacus? Start with the lessons.