48
The numbers 19 and 20
Textbook Part 2, pp. 16–17
GoalBonds of 19 and 20; telling even from odd in two-digit numbers by the last digit.
New words
nineteen · o‘n to‘qqiztwenty · yigirmalast digit · oxirgi raqam
Explanation
19 = 10 + 9; 20 = 10 + 10 — two full tens. Numbers ending in 0, 2, 4, 6, 8 are even; numbers ending in 1, 3, 5, 7, 9 are odd. For example: 16 is even and 19 is odd.
Worked examples
A gardener cut 10 white and 10 red roses: 10 + 10 = 20.
“The sum of 8 and 10 is 17” is a mistake, because 8 + 10 = 18.
Class activity
Pairing flowers: number cards 11 to 20 are mixed up. Children sort them into an “even” box and an “odd” box.
Practice
1
10 + 9 = ?
19
2
20 − 10 = ?
10
3
Find the odd numbers: 12, 15, 17, 18, 20
15, 17
4
A shelf has 7 flower pots and 2 more are added. How many in all?
9