16
Adding (21 + 39)
Textbook: Part 1, lesson 16, pp. 34–35
GoalPractise adding two-digit numbers by splitting into tens and ones (21 + 39).
New words
tens · o‘nliklarones · birliklarmineral resource · foydali qazilmachart · diagramma
Explanation
21 + 39 = (20 + 30) + (1 + 9) = 50 + 10 = 60. First we add the tens, then the ones, and finally the two results. When the ones add up to 10, the answer is a whole ten.
Worked examples
49 + 11 = (40 + 10) + (9 + 1) = 50 + 10 = 60.
36 + 44 = (30 + 40) + (6 + 4) = 70 + 10 = 80.
Class activity
“Mineral mines”: the class splits into three teams. Each team counts the mines on a “map” and writes the total as a sum.
Practice
1
49 + 11 = ?
60
2
36 + 44 = ?
80
3
Team 1 found 32 mineral deposits, team 2 found 18 and team 3 found as many as both together. How many deposits did the three teams find in all?
100
4
t + 8 = 58. t = ?
50