Question

40-39+38-37+……+4-3+2-1

40-39+38-37+……+4-3+2-1大神求教

Answer 1

40–39+38–37...4–3+2–1 =（40-39）+（38-37）+（36-35）+……+（6-5）+（4-3）+（2-1） =1+1+……+1+1 =20

Answer 2

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Answer 3

40-39+38-37+11111111115598888888888