Page 80 - Start Up Mathematics_1

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Numbers 10 to 20

Concept of Tens and Ones

We know numbers from 1–9. We use ones place to write any number from 1 to 9.

1 = 1 one

2 = 2 ones

3 = 3 ones

4 = 4 ones

5 = 5 ones

6 = 6 ones

7 = 7 ones

8 = 8 ones

9 = 9 ones
H T O
To write numbers further, we need two places—tens and ones.

We can count 2-digit numbers on an abacus by using rods

T and O.
Rod O reads in ones. Rod T reads in tens.

We can put a maximum of 9 beads in each rod.

Let’s count further. 9 beads in rod O
show 9 ones or 9.

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