Multiplication and division of decimals

Advanced Math 4 · Unit 14 · decimal-mul-div-intro · Teacher edition

decimal-mul-div-intro

Name ______________________________Date ______________

1.
Compute $2.4 \times 3$ .
Answer: ______________
2.
A ribbon $5.4$ m long is cut into $6$ equal pieces. Ben uses $4$ of the pieces. How many metres of ribbon does Ben use?
Answer: ______________
3.
Each tile is $0.36$ m wide. Five tiles are laid in a row with no gaps. How wide is the row, in metres?
1. (A)
  $0.18$
2. (B)
  $1.8$
3. (C)
  $18$
4. (D)
  $1.5$

Answer key — Multiplication and division of decimals

1.
7.2decimal-mul-div-intro-01
$24 \times 3 = 72$ tenths $= \mathbf{7.2}$ . Estimate: $2 \times 3 = 6$ , and $7.2$ is a bit more.
2.
3.6decimal-mul-div-intro-02
One piece: $5.4 \div 6 = 0.9$ m (since $54 \div 6 = 9$ tenths). Four pieces: $4 \times 0.9 = \mathbf{3.6}$ m.
3.
(B)
$1.8$
decimal-mul-div-intro-03
$36 \times 5 = 180$ hundredths $= 1.80 = \mathbf{1.8}$ m. ( $0.18$ places the point too far left, as if the answer had three decimal places; $18$ forgets the point entirely; $1.5$ multiplies $0.30$ instead of $0.36$ .)