Multiplying Decimals

1
Multiplying Decimals

• Ms. Mayner

2
Strategy 1
405 x 59
405 x 59
405 x 50
405 x 9

4
5
4
3
6
0
2
5
0
2
2
Zero is a place holder. Put a zero in your
answer to hold its place.
(5 x 0) 2 2 Write down the 2.
(5 x 4) 20 Since there are no other numbers to
multiply, write down the 20.
(9 x 0) 4 4 Write down the 4.
5 x 9 45 Put the 5 in the answer and carry the
4 (its really 40) to the next place value (tens)
5 x 5 25 Put the 5 in the answer and carry the
2 (its really 20) to the next place value (tens)
(9 x 4) 36 Since there are no other numbers to
multiply, write down the 36.
3
Strategy 1
405 X 59
405 x 59
405 x 50
405 x 9

4
5
4
3
6
0
2
5
0
2
2
23,895
the final answer is
4
MULTIPLYING DECIMALS Things you need to know

• Do not line up the decimal points!
• Instead, place the number with more digits on
  top.
• Line up the other number underneath, at the
  right.
• Pretend all decimals are whole numbers until the
  very end
• Only look at the decimals when trying to figure
  out where to put the decimal point in your answer

5
Example 5.63 x 3.7
1
Decimal Places
2
4
5.63
two
x
3.7
one
1
1
1
4
39
1
0
9
8
16

1
3
8
0
2
.
three
6
Example 0.53 x 2.618
2.618 has more digits (4) than 0.53 (3), so it
goes on top.
4
3
Decimal Places
2
1
2.618
three
0.53
x
two
1
4
5
8
7
0
0
9
0
13
00
0
0
0
0

.
4
5
7
8
3
1
five
7
Try This 6.5 x 15.3
1
3
1
2
15.3
one
6.5
x
one
1
5
6
7
0
8
1
9

.
5
4
9
9
two
8
Homework

• Multiplying Decimals Page 47 1 d-g, 2 a-d, 9
• 2.5 Multiplying Decimals Page 48-49 3, 5, 9, 11