Review: 3 2s 2 3s 4 2s 2 4s 2+2+2 3+3 2+2+2+2 4+4 groups ( ) in each group 3 2s 2+2+2 2 3s 3+3 4 2s 2+2+2+2 2 4s 4+4

Exploration How many groups of 3? 1 group of 3.

Exploration 3 children in each boat. How many groups of 3？ 2 groups of 3 How many children are rowing? 3+3=6

Exploration Repeated addition Look at the addition sentences, What do you notice? How many groups of 3？ 6 groups of 3 How many children are rowing? 3+3+3+3+3+3=18

How many children are rowing? Exploration The number sentence for 10 groups of 3 is very long. What is a easier way of writing the number sentence? How many groups of 3？ 10 groups of 3 How many children are rowing? 3+3+3+3+3+3+3+3+3+3=30

10 × 3 = 30 Exploration How many groups of 3？ 10 groups of 3 When we add the same things lots of times, it is easier for us to multiply. How many groups of 3？ 10 groups of 3 How many children are rowing? 3+3+3+3+3+3+3+3+3+3=30 10 × 3 = 30 10 times 3 equals 30. There are boats, children in each boat. There are children altogether. 10 3 30

Moving from addition to multiplication

Do you know? William Oughtred The sign “×” was first used by an English mathematician William Oughtred in 1631. Because the multiplication is a special kind of addition, Oughtred used the addition sign.

5 4s How many children are there in the cups altogether? Look at the picture carefully. 5 4s Repeated addition number sentence：____________________________ Multiplication × = , children in one cup, altogether. 4+4+4+4+4=20 5 4 20 5 4 20

6 2s × = 2+2+2+2+2+2=12 6 2 12 6 2 12 How many children are there in the cars altogether？ 6 2s Repeated addition number sentence：_______________________________ Multiplication × = ， children in one car, altogether. 2+2+2+2+2+2=12 6 2 12 6 2 12

1+1+1+1+1+1+1+1+1+1+1+1=12 12 × 1=12 2+2+2+2+2+2=12 6 × 2=12 multiplication number sentence: 1+1+1+1+1+1+1+1+1+1+1+1=12 12 × 1=12 2+2+2+2+2+2=12 6 × 2=12 3+3+3+3=12 4× 3=12 4+4+4=12 3× 4=12 6+6=12 2× 6=12 1 2 3 4 6

True or False (1) 2+2+7=3 ×2 F (2) 8+8+8+8=4 ×8 T (3) 6 5s=6+6+6+6+6 F

Summary Repeated addition number sentences can be transformed into multiplication number sentences.

Challenge 10+10+10+5+5=____×____

Challenge 4 10 10+10+10+5+5=____×____ 10

Challenge 5 5 5 8 5 10+10+10+5+5=____×____