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Sum = ½ × number of numbers × (first number + last number) = ½ × (462 - 408 + 1) × (408 + 462) = ½ × 55 × 870 = 23,925
61 + 67 + 71 + 73 + 79 + 83 + 89 + 97 = 128 + 223 + 269 = 620 unless 61 and 97 are not included then 462
The sum of 3 plus 4 is 7.
SUM means plus 4+7=11
The sum of 10 plus 8 is 18.