8
Review: inverse problems and tables
Textbook: Part 1, lesson 8, pp. 18–19
GoalWriting related (inverse) number sentences; filling a table of letter expressions.
New words
related inverse sum · teskari misoltable · jadvalinsect · hasharotuseful · foydali
Explanation
One addition makes four number sentences: 40 + 6 = 46, 6 + 40 = 46, 46 − 6 = 40, 46 − 40 = 6. In a table we find a + 10, a − 1 and a + a for each value of a.
Worked examples
Related facts of 28 + 14 = 42: 14 + 28 = 42, 42 − 14 = 28, 42 − 28 = 14.
If a = 12: a + 10 = 22, a − 1 = 11, a + a = 24.
Class activity
“Fact family”: each child gets a trio of numbers (for example 14, 28, 42) and writes four number sentences. The fastest correct writer wins.
Practice
1
If 14 + 5 = 19, then 19 − 5 = ?
14
2
If a = 24, then a + a = ?
48
3
If a = 41, then a + 10 = ?
51
4
A silk factory received 8, 12 and 13 boxes of cocoons on three days. Total?
33