53
Adding across ten (continued)
Textbook Part 2, pp. 26–27
GoalUse adding across ten in word problems; swap the addends to make it easier.
New words
hour · soattourist · sayyoheasy way · qulay usul
Explanation
When a big number is added to a small one, swapping them is easier: 3 + 9 = 9 + 3 = 9 + 1 + 2 = 12. Always split off the part that makes 10.
Worked examples
Tourists rode a bus for 6 hours and bikes for 5: 6 + 5 = 6 + 4 + 1 = 11 hours.
Climbing Big Chimyon takes 7 hours and coming down 4: 7 + 4 = 11 hours.
Class activity
Trip map: road sections with hours (5, 6, 4…) are on the board. Children pick two sections and find the total time by making ten.
Practice
1
4 + 8 = ?
12
2
6 + 7 = ?
13
3
5 + 9 = ?
14
4
Can a square and a circle each be cut into two equal halves with one straight cut?
Yes, both