Question
$10 + 11 + 12 + 13 + 14 + 15 + 16 + 17 + 18 + 19 + 20$
✓
Answer
$10 + 11 + 12 + 13 + 14 + 15 + 16 + 17 + 18 + 19 + 20$
$10 + 20 = 30$
$1 + 9 = 10$
$2 + 8 = 10$
$3 + 7 = 10$
And,
$4 + 6 = 10$
Therefore,
$(10 + 20) + (11 + 19) + (12 + 18) + (13 + 17) + (14 + 16)$
$= 30 + 30 + 30 + 30 + 30 + 15$
$= 150 + 15$
$= 165$
$10 + 20 = 30$
$1 + 9 = 10$
$2 + 8 = 10$
$3 + 7 = 10$
And,
$4 + 6 = 10$
Therefore,
$(10 + 20) + (11 + 19) + (12 + 18) + (13 + 17) + (14 + 16)$
$= 30 + 30 + 30 + 30 + 30 + 15$
$= 150 + 15$
$= 165$
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