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$23 \times 21$ is the same as
$$(20 \times 21) + (3 \times 21)$$
which is the same as
$$((20 \times 20) + (20 \times 1)) + ((3 \times 20) + (3 \times 1))$$
Can you figure out where each of these four products appears in the different methods?
Can you deconstruct $246 \times 34$ in the same way?
EWWNP means Exploring Wild and Wonderful Number Patterns Created by Yourself! Investigate what happens if we create number patterns using some simple rules.
Place four pebbles on the sand in the form of a square. Keep adding as few pebbles as necessary to double the area. How many extra pebbles are added each time?