To multiply a number between 10 and 20 by a 1-digit number, multiply the 1-digit number by 10, then multiply it by the second digit in the 2-digit number, and add the products. Example: 13 × 6 ĺ (6 × 10) + (6 × 3) = 60 + 18; answer: 78.
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feasthat - (no access) - Secrets of Mental Math (guidebook).pdf, p12
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