To square a 2-digit number that ends in 5, multiply the first digit in the number by the next higher digit, then attach 25 at the end. Example: 35 * 2 => 3 × 4 = 12; answer: 1225. For 3-digit numbers, multiply the first two numbers together by the next higher number, then attach 25. Example: 305 2 ĺ 30 × 31 = 930; answer: 93,025.
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feasthat - (no access) - Secrets of Mental Math (guidebook).pdf, p11
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