Written methods of multiplication Let’s investigate
Vocabulary
The numbers in the triangles are connected by a rule.
121
?
3 " 363
Use the first triangle to find the rule. Then use the rule to complete the other two triangles. 363
121
1
2
777
3
482
9
product: the answer you get when you multiply two or more numbers together. product
7 ! 8 " 56 7
Estimate first, then calculate: (a) 318 ! 2
(b) 426 ! 3
(c) 512 ! 7
(d) 936 ! 8
(e) 671 ! 9
(f) 384 ! 6
This example shows one method to caluclate 5.7 ! 4 Estimate: 5.7 ! 4 is approximately 6 ! 4 " 24 !
5
0.7
4
20
2.8
20 # 2.8 " 22.8
22.8 is close to 24, so 22.8 is a reasonable answer. Use this method, or any other method, to work out the following: (a) 4.9 ! 5
(b) 6.3 ! 7
(c) 3.8 ! 8
(d) 5.7 ! 9
(e) 4.3 ! 6
(f) 4.5 ! 9
3
Calculate double 15.5
4
A packet contains 1.5 kg of rice. How much rice is in five packets?
16
Unit 1A: Core activity 3.2 Written methods of multiplication