27
Adding (28 + 14)
Textbook: Part 1, lesson 26, pp. 56–57
GoalPractise the 28 + 14 method; doubles and an equation.
New words
pattern · qonuniyatchain · zanjirearphones · quloqchincounter (shop) · peshtaxta
Explanation
We practise adding two-digit numbers a lot. We look for a pattern: 19 + 19 = 38, 28 + 28 = 56, 37 + 37 = 74. The first addend grows by 9 each time. To check an addition we can subtract one addend from the sum.
Worked examples
46 + 17 = (40 + 10) + (6 + 7) = 50 + 13 = 63. Check: 63 − 17 = 46.
A box has 50 earphones, 35 are blue. Red ones: 50 − 35 = 15.
Class activity
“Continue the chain”: 19 + 19, 28 + 28, 37 + 37 ... Children write the next two sums (46 + 46, 55 + 55) and calculate them.
Practice
1
29 + 25 = ?
54
2
46 + 17 = ?
63
3
A box has 50 earphones, 35 are blue and the rest are red. How many are red?
15
4
25 and 18 phones stand on a counter. 12 were sold. How many are left?
31