1
Doubles and near doubles
Discover Mathematics P2: Term 1, Lessons 11–20
GoalAdd a number to itself, and use a double to add numbers that are one apart.
New words
double · a number added to itself, like 4 + 4near double · two numbers that are one apart, like 6 + 7sum · the answer when we add
Explanation
A double is a number added to itself: 4 + 4 = 8. Learn the doubles up to 10 + 10 = 20. They help you add fast. A near double is two numbers that are one apart, such as 6 + 7. Find the double of the smaller number, then add 1: 6 + 6 = 12, and 12 + 1 = 13. So 6 + 7 = 13.
Worked examples
Both hands show 5 fingers. 5 + 5 = 10. That is a double.
Youssef has 6 pears in one basket and 7 pears in another. 6 + 6 = 12, then add 1 more: 12 + 1 = 13 pears.
To add 8 + 9, think 8 + 8 = 16. Then add 1 more. 16 + 1 = 17.
Class activity
Doubles game. Use a die or number cards from 1 to 10. Turn over a card and say its double. Then turn over two cards that are one apart, such as 7 and 8, and say the near double.
Practice
1
Seif has 7 kites and Mina has 7 kites. How many kites are there in all?
14 (7 + 7 = 14)
2
What is 9 + 9?
18
3
What is 6 + 7? Use the double 6 + 6.
13 (6 + 6 = 12, then 12 + 1 = 13)
4
What is 4 + 5?
9 (4 + 4 = 8, then 8 + 1 = 9)
5
Farida has 10 beads on a string and 10 beads on another string. How many beads does she have?
20