To multiply two 2-digit numbers that have the same ¿ rst digits and last digits that sum to 10, multiply the ¿ rst digit by the next higher digit, then attach the product of the last digits in the original two numbers. Example: 84 × 86 ĺ 8 × 9 = 72 and 4 × 6 = 24; answer: 7224.
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feasthat - (no access) - Secrets of Mental Math (guidebook).pdf, p12
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