Four operations of decimals

Answer key — Four operations of decimals

1. 1.
   8.55decimal-four-operations-01

   $4.80 + 3.75 = \mathbf{8.55}$.

2. 2.
   3.125decimal-four-operations-02

   $1.25 \div 0.4 = 12.5 \div 4 = \mathbf{3.125}$. Sense check: $0.4$ is less than $1$, so the answer is bigger than $1.25$; and $3 \times 0.4 = 1.2$, close to $1.25$. ✓

3. 3.
   (B)

   $0.09$

   decimal-four-operations-03

   $0.3 \times 0.3 = 0.09$ m²: one place plus one place is two places. Sense check: $0.3 < 1$, so $0.3 \times 0.3$ must be less than $0.3$, which rules out $0.9$. Answer $\mathbf{0.09}$. ($0.6$ is $0.3 + 0.3$; $9$ and $0.009$ have the wrong number of decimal places.)