# Slavonic Abacus

Achievement Objectives
NA2-4: Know how many ones, tens, and hundreds are in whole numbers to at least 1000.
Specific Learning Outcomes

Recall the number of tens and hundreds in 100s and 1000s.

Description of Mathematics

Number Framework Stage 5

Activity

Out of sight of the students create a “ty” number on the abacus. Turn the abacus around and show the students the beads briefly. Do not allow time to count by tens. Encourage the students to recognise the numbers of rows from their ability to recognise ones. For example, if the number of beads is 60, they need to see instantly that there are six rows of 10. They do this by spotting five rows of a pair of colours and one other row with the other pair of colours. And they know 5 + 1 = 6. If the students have to count 10, 20, 30, 40, 50, 60, this possibly indicates that the

students do not realise six tens are “sixty”. Help them to focus on place-value structure by asking, “How many rows of 10 were there?” If necessary show the beads again, and say, “There are six tens”.

#### Activity

Repeat, but this time include single beads, for example, show 68 briefly. Expect the students to recognise this quickly, without any counting, as a collection of six rows of 10 and eight single beads and say “68”.”