Multiply a two-digit number by a single-digit number (don’t remember)

### 1.1. Knowledge to remember

**12 x 3 = ?**

12 + 12 + 12 = 36

12 x 3 = 36

\({\frac{{ \times \begin{array}{*{20}{c}}

{twelfth}\\

{\,\,3}

\end{array}}}{{\,\,36}}}\)

3 times 2 equals 6, write 6.

3 times 1 equals 3, write 3.

**The multiplication steps are:**

- Set count
- Calculation: Multiply by the units digit then multiply by the tens digit

### 1.2. Solving Textbook Exercises

**Lesson 1:** Calculate

\( \times \underline {\begin{array}{*{20}{c}}

{24}\\

{\,\,2}

\end{array}} \) \( \times \underline {\begin{array}{*{20}{c}}

{22}\\

{\,\,4}

\end{array}} \) \( \times \underline {\begin{array}{*{20}{c}}

{11}\\

{\,\,5}

\end{array}} \) \( \times \underline {\begin{array}{*{20}{c}}

{33}\\

{\,\,3}

\end{array}} \) \( \times \underline {\begin{array}{*{20}{c}}

{20}\\

{\,\,4}

\end{array}} \)

**Solution guide:**

\(\frac{{ \times \begin{array}{*{20}{c}}

{24}\\

{\,\,2}

\end{array}}}{{\,\,\,48}}\) \(\frac{{ \times \begin{array}{*{20}{c}}

{22}\\

{\,\,4}

\end{array}}}{{\,\,\,88}}\) \(\frac{{ \times \begin{array}{*{20}{c}}

{11}\\

{\,\,5}

\end{array}}}{{\,\,\,55}}\) \(\frac{{ \times \begin{array}{*{20}{c}}

{33}\\

{\,\,\,3}

\end{array}}}{{\,\,\,99}}\) \(\frac{{ \times \begin{array}{*{20}{c}}

{20}\\

{\,\,4}

\end{array}}}{{\,\,\,80}}\)

**Lesson 2:** Calculate then calculate

a) 32 x 3 b) 42 x 2

11 x 6 13 x 3

__Solution guide:__

- Line up the second factor with the units of the first factor
- Calculating from right to left, multiply the second factor by the digits in the units and tens places of the first factor, respectively.

a) \(\frac{{ \times \begin{array}{*{20}{c}}

{32}\\

{\,\,3}

\end{array}}}{{\,\,\,96}}\) \(\frac{{ \times \begin{array}{*{20}{c}}

{11}\\

{\,\,6}

\end{array}}}{{\,\,\,66}}\) b) \(\frac{{ \times \begin{array}{*{20}{c}}

{42}\\

{\,\,2}

\end{array}}}{{\,\,\,84}}\) \(\frac{{ \times \begin{array}{*{20}{c}}

{13}\\

{\,\,3}

\end{array}}}{{\,\,\,39}}\)

**Lesson 3:** Each box contains 12 crayons. How many crayons are there in 4 such boxes?

**Solution guide:**

Number of pens in

$4$box = Number of pens in each box multiplied by

*Solution*

Number of crayons in

$4$the box is:

$48$

(Crayons)

Answer:

Crayons.

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