Question

Do it mentally and write the answers.

• 2 × 6 = __________
• 20 × 6 = __________
• 2 × 60 = __________
• 3 × 42 = __________
• 4 × 80 = __________
• 4 × 81 = __________
• 9 × 25 = __________
• 31 × 9 = __________

Answer 1

• 12
• 120

We do it in the following manner:
2 times 6 is 12.
20 times 6 is 120.

• 120
• 126

We do it in the following manner:
3 $\times$ 40 = 120
Also, 3 $\times$ 2 = 6
So,
$$\begin{gathered} \begin{array}{ccc}1& 2& 0\\ +& & 6\end{array} \\ \underline{\overline{\begin{array}{ccc}1& 2& 6\end{array}}} \end{gathered}$$

• 320

We do it in the following manner:
4 times 8 is 32.
4 times 80 is 320.

• 324

We do it in the following manner:
4 $\times$ 80 = 320
Also, 4 $\times$ 1 = 4
So,
$$\begin{gathered} \begin{array}{ccc}3& 2& 0\\ +& & 4\end{array} \\ \underline{\overline{\begin{array}{ccc}3& 2& 4\end{array}}} \end{gathered}$$

• 225

We do it in the following manner:
9 $\times$ 20 = 180
Also, 9 $\times$ 5 = 45
So,
$$\begin{gathered} \begin{array}{ccc}& & \\ \stackrel{1}{1}& 8& 0\\ +& 4& 5\end{array} \\ \underline{\overline{\begin{array}{ccc}2& 2& 5\end{array}}} \end{gathered}$$

• 279

We do it in the following manner:
30 $\times$ 9 = 270
Also, 1 $\times$ 9 = 9
So,
$$\begin{gathered} \begin{array}{ccc}& & \\ 2& 7& 0\\ +& 0& 9\end{array} \\ \underline{\overline{\begin{array}{ccc}2& 7& 9\end{array}}} \end{gathered}$$