Download Multiplying whole numbers

STRAND: Number
TOPIC:
Whole numbers
Multiplying whole numbers
Short multiplication is used when we need to multiply by numbers less than or equal to 12. To multiply by numbers greater than
12, long multiplication is used.
WORKED Example 1
Calculate 735 × 7 using short multiplication.
THINK
1
2
3
4
WRITE
2 3 3
735
×
7
5313435
Set out the question.
Multiply 7 by the number in the units place: 7 × 5 = 35. Put 5 in the
units place (of the answer part) and carry the 3 to the tens column.
Multiply 7 by the number in the tens place: 7 × 3 = 21. Adding the
‘carry over’ gives: 21 + 3 = 24. So put 4 in the tens place (of the
answer part) and carry the 4 to the hundreds column.
Multiply 7 by the number in the hundreds place: 7 × 7 = 49. Adding
the ‘carry over’ gives: 49 + 2 = 51. Write down 51 (in the answer
part) so that 1 is in the hundreds and 5 is in the thousands column.
WORKED Example 2
Calculate 7623 × 46 using long multiplication.
THINK
1
2
3
4
WRITE
Set out the question one number under the other and underline.
Multiply 7623 by 6 (that is, by units) using the method described in
worked example 1. Record your answer under the line.
Move to the next line. Put a 0 in the units column; multiply 7623 by
4 (that is, by tens) and record your answer next to 0.
Underline and add the two parts together to find the final answer.
3 1 1 1
×
7623
416
1 1 1 1
45738
2 1 1 1
7623
416
1 1 1 1
45738
31014191210
×
7161213
×
416
1 1 1 1
45738
+ 31014191210
31510161518
Try these
1 Calculate the following using short multiplication.
a 63 × 4
b 47 × 5
c 58 × 3
f 428 × 4
g 563 × 7
h 367 × 5
k 6750 × 4
l 8253 × 9
m 7196 × 8
2 Calculate the following using long multiplication.
a 73 × 16
b 49 × 24
c 54 × 37
f 156 × 29
g 641 × 36
h 723 × 17
k 7462 × 135
l 3758 × 469
m 2183 × 516
d 76 × 6
i 845 × 6
n 4936 × 3
e 62 × 9
j 956 × 3
o 5039 × 5
d 35 × 18
i 824 × 53
n 9241 × 372
e 68 × 59
j 395 × 48
o 4569 × 284
 John Wiley & Sons Australia, Ltd 2001