To multiply two numbers that are both between 10 and 20, add the first number and the last digit of the second number, multiply the result by 10, then add that result to the product of the last digits in both numbers of the original problem. Example: 13 × 14 ĺ 13 + 4 = 17, 17 × 10 = 170, 3 × 4 = 12, 170 + 12 = 182; answer: 182.
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feasthat - (no access) - Secrets of Mental Math (guidebook).pdf, p12
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