Soroban unit 6: Multiplication
Times facts, then 2-digit by 1-digit and 2-digit by 2-digit products, added part by part on the soroban.
Multiplying with partial products
This course multiplies on the soroban by adding partial products. For 23 × 4, multiply each digit of 23 by 4 and add the results on the rods: 20 × 4 = 80, then 3 × 4 = 12, so the soroban shows 92. For 23 × 12 there are four partial products: 20 × 10, 3 × 10, 20 × 2 and 3 × 2, that is 200, 30, 40 and 6, which make 276.
Classic soroban multiplication also sets the two numbers on separate rods and places each product by the unit rod; the partial products and the adding are the same. Here the soroban does all of the adding, so you only need one times fact at a time.
The facts come first
Partial products are only as quick as the times tables behind them. The unit starts with a few facts, and the mental round is facts only. If 7 × 8 or 6 × 9 still makes you pause, Sum Racer on the games page drills times facts at speed.
Checking
Round to check any product: 47 × 6 is a little less than 50 × 6 = 300, so 282 looks right. In Your turn, the step line always shows which partial product comes next.