Question

1. $5 \times 4 = \underline{\quad\quad}$

(\underline{\quad\quad} $\times$ \underline{\quad\quad}) + (\underline{\quad\quad} $\times$ \underline{\quad\quad})
\underline{\quad\quad} + \underline{\quad\quad}

Explanation:

Step1: Calculate \(5 \times 4\)

We know that \(5\times4\) can be decomposed. Let's choose to decompose 5 into 3 and 2 (or other numbers, here we use 3 and 2 as an example). So we can write \(5\times4=(3\times4)+(2\times4)\).

Step2: Calculate each product

First, calculate \(3\times4 = 12\), and then calculate \(2\times4=8\).

Step3: Sum the products

Then sum these two results: \(12 + 8=20\), and also \(5\times4 = 20\). (Note: The decomposition can also be other forms, like \(4\times4+(1\times4)\) etc., but here we take one possible decomposition.)

Answer:

First, \(5\times4=\boldsymbol{20}\)

For the decomposition: \((\boldsymbol{3}\times\boldsymbol{4})+(\boldsymbol{2}\times\boldsymbol{4})\) (or other valid decompositions like \((4\times4)+(1\times4)\) etc.)

Then \(\boldsymbol{12}+\boldsymbol{8}\) (corresponding to the above decomposition, if using \(3\times4\) and \(2\times4\))