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LEVEL 2
Russian Multiplication
How It Works
Step 1 — Two Columns
Write the two numbers side by side. Left column = number to halve. Right column = number to double.
Step 2 — Halve & Double
Keep halving the LEFT (drop remainders) and doubling the RIGHT until the left reaches 1.
Step 3 — Mark Odd Rows
Cross out any row where the LEFT number is even. Keep only the ODD rows.
Step 4 — Sum Right Column
Add up the RIGHT values from all kept (odd) rows. That is your answer!
Why does it work?
Halving the left converts it to binary. Each odd row corresponds to a "1" bit. Doubling the right scales the value for that bit position. It's ancient math meets binary computing!
Example: 47 × 18
18 + 36 + 72 + 144 + 576 = 846 ✓